M&A Due Diligence for SMEs

Context

Portugal recorded 602 M&A transactions in 2024, with an aggregate value of €12.6 billion, according to TTR Data. Only 41% of these deals disclosed their value — an information asymmetry that particularly disadvantages SME buyers lacking internal resources for rigorous due diligence. M&A due diligence is not a compliance audit; it is the process that transforms uncertainty into a defensible price, deal structure, and integration plan. When properly conducted, due diligence answers three questions: what price makes sense given the identified risk, what deal structure protects the buyer without jeopardising the transaction, and which critical dependencies will shape the first 100 days post-closing.

SMEs account for 99.9% of Portuguese businesses and generated €319.2 billion in turnover in 2023, yet they often lack transactional experience. Many treat due diligence as a legal formality, delegate it to auditors without a strategic briefing, or limit themselves to validating accounts without questioning EBITDA sustainability, customer concentration, or operational dependencies. The result: post-closing surprises that destroy value, disputed price adjustments, poorly calibrated earn-outs, or delayed integration due to lack of early mapping of systems and processes.

This article examines due diligence as a management tool, not merely a compliance exercise. It analyses the five workstreams — financial, tax, legal, operational, and commercial — and demonstrates how findings inform valuation, deal structure, and integration planning. It draws on Portuguese transactional market data, international M&A benchmarks, and research evidence on post-acquisition value destruction to build a decision model useful for CEOs, CFOs, and boards of SME buyers or sellers.

The State of the Evidence

Research on M&A is unanimous on one point: most acquisitions fail to create value for the buyer. Christensen et al. (Harvard Business Review, 2011) documented that 70–90% of acquisitions do not achieve stated objectives, with value destruction concentrated in three stages: overvaluation during due diligence, deal structure misaligned with risk, and integration failure within the first 12 months. Effective due diligence reduces risk at all three stages, but evidence shows that SMEs tend to underinvest in this phase.

Bain & Company (2020) analysed 250 mid-market transactions in Europe and found that companies conducting detailed operational due diligence — mapping processes, IT systems, supplier and key employee dependencies — were 2.3 times more likely to achieve the synergies stated in the business case. The study identified three recurring failures among SME buyers: lack of EBITDA normalisation (personal expenses, one-offs, off-market salaries), insufficient validation of the commercial pipeline, and failure to map critical IT systems before defining the integration plan.

PwC (Global M&A Trends, 2024) reported that 63% of global deals included price adjustment mechanisms (working capital peg, net debt adjustment, earn-out) in 2023–2024, up from 48% in 2015–2019. The increasing sophistication of deal structures reflects greater risk awareness, but also greater complexity in due diligence: validating an earn-out requires auditable commercial projections, not just historical accounts. The report highlights that poorly calibrated earn-outs — lacking measurable milestones or with post-closing information asymmetry — result in litigation in 40% of cases.

Deloitte (M&A Trends Report 2025, Europe) documented that 58% of European mid-market transactions in 2024 included early vendor due diligence (VDD), up from 32% in 2019. VDD reduces negotiation time, increases transparency, and can raise the final price by 5–15% by reducing the risk discount. However, the effectiveness of VDD depends on the advisor's independence: if the seller controls the scope or presentation, the buyer should conduct parallel confirmatory due diligence.

KPMG (European M&A Outlook 2025) identified five red flags that justify walking away or a material price adjustment: customer concentration above 40% in a single client, unprovisioned tax or labour liabilities exceeding 10% of EBITDA, critical founder dependency without a documented succession plan, verbal contracts or contracts lacking change-of-control clauses with key clients, and obsolete IT systems without a migration roadmap. The study shows that SME buyers tend to tolerate these risks in exchange for a price discount, but underestimate post-closing mitigation costs.

There is disagreement over the optimal scope of due diligence. McKinsey (2022) argues that operational and commercial due diligence should precede financial due diligence, as valuation only makes sense after validating revenue and margin sustainability. BCG (2023) contends that early financial due diligence allows non-viable deals to be discarded before investing in operational workstreams. Evidence suggests that the optimal sequence depends on sector and buyer type: strategic buyers benefit from early operational DD; financial buyers prioritise financial and tax DD.

Mechanisms

Financial Due Diligence: EBITDA Normalisation and Asset Quality

Financial due diligence validates three dimensions: EBITDA sustainability, asset and liability quality, and cash flow robustness. EBITDA normalisation is the critical exercise: identifying non-recurring costs (restructuring, litigation, one-off capex), owner’s personal expenses (above- or below-market salaries, benefits in kind, life insurance), and costs not reflected in audited accounts (deferred maintenance, postponed IT investment, pending compliance). Damodaran (NYU Stern) documents that normalised EBITDA adjustments range from 10–30% in SMEs, with direct impact on valuation.

Asset quality covers three areas: tangible fixed assets (physical assets — condition, remaining useful life, need for replacement capex), intangible assets (intellectual property, registered trademarks, licensed vs. internally developed software, exclusivity contracts), and current assets (inventory — obsolescence, turnover, seasonality; receivables — aging, provisions, debtor concentration). Hidden liabilities include tax contingencies (corporate tax, VAT, social security), environmental (soil contamination, industrial waste), labour (pending lawsuits, unprovisioned severance), and contractual (warranties, penalties, take-or-pay clauses).

Sustainable operating cash flow is the final test. Audited accounts show accounting profit; due diligence validates whether that profit converts to cash. Three warning signs: working capital growing faster than sales (indicating deteriorating receivables or inventory), recurring capex exceeding depreciation (sign of aging assets), and reliance on short-term financing to cover ongoing operations. Companies with PME Líder status (IAPMEI, 2024: 13,394 companies, average financial autonomy 59.4%) tend to have more robust cash flow, but due diligence should validate this on a case-by-case basis.

Tax Due Diligence: Contingencies, Compliance, and Incentive Eligibility

Tax due diligence identifies three types of risk: unprovisioned contingencies, sub-optimal tax structure, and loss of eligibility for incentives post-closing. Tax contingencies include corporate tax (transfer pricing, thin capitalisation, cost deductibility), VAT (reversal of deductions, intra-community operations, service provision), social security (reclassified freelancers, non-compliant internships), and local taxes (IMI, IMT in restructurings). Due diligence should request debt-free certificates, tax inspections from the last 4 years, and tax advisor opinions on aggressive tax positions.

Eligibility for tax incentives — SIFIDE II (corporate tax deduction of 32.5% base + 50% incremental up to €1.5M, extended until end of 2026), RFAI (30% deduction for investments up to €15M in the North/Centre/Alentejo/Madeira/Azores) — can be material for R&D or capex-intensive companies. Due diligence should validate whether declared incentives have been audited, if there is a risk of clawback, and whether the post-closing structure maintains eligibility. Change of control may trigger a reassessment of tax benefits by the Tax Authority.

Post-closing tax structure deserves early analysis. Share deals vs. asset deals have distinct tax implications: share deals retain the target’s tax history (including contingencies), asset deals allow a step-up in tax basis but may trigger capital gains tax for the seller. The choice depends on risk appetite, ability to absorb tax loss carryforwards, and negotiation of indemnity caps in the SPA (Share Purchase Agreement).

Legal Due Diligence: Contracts, Intellectual Property, and Labour Compliance

Legal due diligence covers five workstreams: commercial contracts (clients, suppliers, distributors), intellectual property and intangible assets, litigation and contingencies, labour compliance, and corporate structure. Key contracts should be reviewed for term, change-of-control clauses, exclusivity, penalties, warranties, and termination rights. Verbal contracts or those lacking change-of-control clauses increase the risk of losing clients or suppliers post-deal — due diligence should map these contracts and plan early communication.

Intellectual property includes registered trademarks (INPI), patents, industrial design, software (licensed vs. internally developed, open-source compliance), databases, and know-how. Due diligence should validate ownership, registration, third-party licences, and assignment agreements with employees. In sectors such as ICT (Portuguese market of €16 billion in 2024, according to APDC) or agri-food (exports of €8.19 billion, +8.73% YoY), intellectual property may represent a material share of company value.

Labour compliance examines employment contracts, company agreements, pending labour disputes, health and safety, and eligibility for co-financed training programmes (Portugal 2030 — Pessoas 2030, €5.7 billion allocation). Due diligence should identify key employees, validate non-compete clauses, and map the risk of post-closing departures. Retention of critical talent may justify incentive retention packages or earn-outs tied to continued employment.

Operational Due Diligence: Processes, IT Systems, and Critical Dependencies

Operational due diligence maps how the company creates value: production processes, supply chain, IT systems, installed capacity, and critical dependencies on people or suppliers. The goal is threefold: validate operational margin sustainability, identify cost synergies, and map dependencies that will shape the integration plan. Companies with documented processes (ISO 9001, lean manufacturing, continuous improvement) facilitate due diligence and integration; companies without documentation require mapping from scratch.

IT systems are often the integration bottleneck. Due diligence should inventory ERP, CRM, production systems (MES, SCADA), infrastructure (on-premise vs. cloud), software licences, and maintenance contracts. Obsolete systems or lack of ERP hinder consolidation of financial reporting, inventory visibility, and process integration. Due diligence should estimate migration or replacement costs — an SME ERP can cost €50k–€300k and take 6–18 months to implement.

Critical dependencies include single-source suppliers, key employees without identified successors, and assets shared with other companies in the seller’s group. Due diligence should map these dependencies, validate supply contracts, and plan mitigation (dual sourcing, backup hiring, transitional services agreement with the seller). Sectors such as automotive components (exports of €11.785 billion in 2024, according to AFIA) or metalworking (annual turnover of €35 billion, AIMMAP) have complex supply chains requiring deep operational due diligence.

Commercial Due Diligence: Clients, Pipeline, and Competitive Positioning

Commercial due diligence validates revenue sustainability: client portfolio (concentration, churn, lifetime value), commercial pipeline (lead quality, conversion rate, sales cycle), competitive positioning (market share, differentiation, barriers to entry), and distribution channels (direct vs. indirect, exclusivity, margin). Client concentration above 30–40% of turnover in a single client is a material red flag — losing that client can invalidate the business case.

The commercial pipeline must be auditable. Due diligence should request CRM data, historical conversion by lead source, opportunity aging, and validation of signed vs. verbal contracts. Sales projections in earn-outs should be based on validated pipeline, not aspirations. B2B sectors such as metalworking or auto components have long sales cycles (6–18 months) and concentrated pipelines — due diligence should validate each material opportunity.

Competitive positioning examines three dimensions: market share (absolute and relative to the top 3 competitors), differentiation (price, quality, service, innovation), and barriers to entry (regulation, capital, technology, distribution network). Due diligence should include client interviews (with seller’s consent), competitor analysis, and validation of claims of technological or commercial leadership. Companies with Inovadora COTEC status (1,056 companies in 2024, R&D investment above 10% of GVA) tend to have stronger differentiation, but due diligence should validate its translation into pricing power or market share.

The Portuguese Case

The Portuguese transactional market has three characteristics that shape SME due diligence: sector concentration, prevalence of family businesses, and high information asymmetry. According to TTR Data, the most active M&A sectors in 2024 were Real Estate (54 deals) and Internet/Software/IT Services (35 deals), but most SMEs transact in traditional sectors — agri-food, auto components, metalworking, textiles — where process and system documentation is often limited.

Family businesses represent about 75% of Portuguese companies, 65% of GDP, and 50% of total employment, according to the Family Business Association. Due diligence in family businesses faces three specific challenges: blurred boundaries between personal and business assets (real estate, vehicles, insurance), off-market family salaries (above or below), and undocumented strategic decisions (investments, divestments, partnerships). EBITDA normalisation is critical: personal expenses can represent 10–20% of reported EBITDA in family SMEs.

Information asymmetry is high: only 41% of M&A transactions in Portugal disclosed value in 2024. This opacity penalises SME buyers, who lack valuation benchmarks and deal structure references. Specialist M&A consultancies for SMEs — such as Macro Consulting — provide access to comparable transaction data and SPA negotiation expertise, but many SMEs attempt to conduct due diligence internally or delegate it to auditors without a strategic briefing.

The Portuguese regulatory context facilitates due diligence in some areas and complicates it in others. Debt-free certificates (Tax Authority, Social Security, courts) can be obtained online within 24–48 hours. The Commercial Registry is public and accessible via Empresa na Hora. However, the lack of a centralised register of commercial contracts or intellectual property (except trademarks and patents at INPI) requires case-by-case validation. Legal due diligence should include searches for litigation in judicial and arbitration courts, tax enforcement, and liens.

Tax and financial incentives affect valuation and deal structure. Companies eligible for SIFIDE II or RFAI may have added value if the buyer maintains eligible activities. Companies funded by Portugal 2030 (total allocation €23 billion, €7.9 billion approved by April 2026) or by venture capital funds (122 rounds, €886 million in 2024, according to TTR Data) may have reporting obligations or repayment clauses in case of change of control — due diligence should validate financing contracts and post-closing eligibility.

Export sectors — footwear (€1.702 billion in exports, 90% of production), wine (€899 million Jan–Nov 2024), agri-food (€8.19 billion) — face currency, regulatory, and geopolitical exposure that commercial due diligence must map. The geographic concentration of exports (Spain 28–39% in various sectors, according to 2024 sector data) increases the risk of external demand shocks. Due diligence should validate market diversification, medium-term contracts, and currency hedging.

Management Decisions

Useful due diligence is not a compliance checklist; it is a decision tool that informs three critical choices: price, deal structure, and integration plan. The first decision — price — depends on normalised EBITDA, asset quality, sustainable cash flow, and identified risk. Adjustments to normalised EBITDA (one-offs, off-market salaries, personal expenses) can alter valuation by 10–30%. Due diligence should produce a bridge between reported and normalised EBITDA, with each adjustment documented and auditable.

Valuation multiples vary significantly by sector. Damodaran (NYU Stern) publishes annual EV/EBITDA multiples by industry: high-growth sectors (software, medtech) transact at 12–18× EBITDA; mature sectors (metalworking, auto components) at 5–8× EBITDA; declining sectors (traditional retail, printing) at 3–5× EBITDA. Commercial due diligence should validate competitive positioning and growth prospects to justify a multiple within the sector range. Companies with organic growth above 10% per year, EBITDA margin above the sector median, and low client concentration justify a multiple in the upper quartile.

The second decision — deal structure — should reflect risk identified in due diligence. Tax, labour, or environmental contingencies justify price adjustment mechanisms (working capital peg, net debt adjustment, indemnity escrow). Uncertainty about revenue sustainability justifies an earn-out tied to future performance — but earn-outs only work if milestones are measurable, auditable, and aligned with the buyer’s operational control. The technical structure of earn-outs should be negotiated during due diligence, not after the LOI (Letter of Intent).

Working capital peg and net debt definitions are frequent sources of post-closing disputes. Due diligence should define normalised working capital (average of the last 12–24 months, adjusted for seasonality), net debt (financial debt minus cash, including or excluding leasing, factoring, bank guarantees), and the adjustment mechanism (euro-for-euro, threshold, cap). The SPA should include a timetable for completion accounts, objection period, and dispute resolution mechanism (expert determination vs. arbitration).

The third decision — integration plan — starts during due diligence, not after closing. Operational due diligence should map quick wins (immediate cost synergies — function duplication, supplier contract renegotiation, facility consolidation), critical dependencies (key employees, single-source suppliers, shared IT systems), and execution risks (cultural resistance, talent loss, client attrition). The Day 1 integration plan should include stakeholder communication (clients, suppliers, team), appointment of an integration manager, and definition of post-closing governance.

Early identification of key employees and design of incentive retention packages reduces the risk of post-deal departures. Due diligence should map the organisational chart, identify single points of failure (people without backup), and validate employment contracts, non-compete clauses, and eligibility for stock options or phantom equity. Retention of critical talent may justify an earn-out tied to continued employment or a retention bonus paid in tranches over 12–24 months.

Integration of IT systems, financial processes, and reporting should be planned during due diligence. Operational due diligence should map critical systems (ERP, CRM, MES, SCADA), validate software licences, identify IT dependencies on the seller’s group, and estimate migration cost and timeline. Companies without ERP or with obsolete on-premise systems may require material post-closing investment — due diligence should include this cost in the business case and integration plan. Digital transformation post-acquisition can be an opportunity for modernisation, but should be phased to avoid overloading the organisation.

Three diagnostic questions for decision-makers before starting due diligence: (1) Are we clear on the business case — what synergies do we expect, what risks are we willing to accept, what is the maximum price that makes sense? (2) Do we have internal capacity to conduct due diligence or do we need an external advisor — and for which workstreams? (3) Do we have a preliminary integration plan or are we buying without a vision for post-closing value creation? Due diligence is only useful if it informs decisions; if the buyer has already decided on price and structure before starting DD, the process becomes an expensive and pointless formality.

Limits and Unknowns

The evidence on M&A due diligence has three limitations. First, most studies focus on large or listed transactions; there is a lack of research on unlisted SMEs, where information asymmetry is greater and resources for DD are scarcer. Second, evidence on the effectiveness of vendor due diligence is mixed: VDD can speed up the process and increase price, but can also conceal risks if the advisor is not independent. Third, the relationship between due diligence cost and post-closing value creation is not linear: excessively detailed DD can delay the deal without reducing material risk, while insufficient DD can leave red flags unidentified.

The arguments in this article do not apply to three contexts. First, distressed or opportunistic acquisitions, where the buyer accepts high risk in exchange for a material discount — in these cases, due diligence may be limited to validating asset ownership and absence of legal impediments. Second, acquisitions of specific assets (real estate, patents, client portfolios) without operational continuity — here, due diligence focuses on the asset, not the company. Third, acquisitions between companies in the same group or with a history of collaboration — information asymmetry is lower and due diligence can be simplified.

Unknowns remain regarding the optimal timing of due diligence (before or after LOI), ideal scope by sector (the weight of operational vs. commercial DD in services vs. industry), and the trade-off between DD cost and residual risk. Future research should focus on SMEs, compare the effectiveness of VDD vs. buyer DD, and quantify the return on investment in due diligence by workstream. Until then, decision-makers should calibrate DD scope to perceived risk, transaction materiality, and internal post-closing integration capacity.

Sources

• TTR Data (2024), Relatório Anual 2024 Mercado Transacional Português. Available at ttrecord.com
• Christensen, C. M., Alton, R., Rising, C., & Waldeck, A. (2011), "The Big Idea: The New M&A Playbook", Harvard Business Review, March 2011
• Bain & Company (2020), M&A in Europe: Lessons from 250 Mid-Market Deals
• PwC (2024), Global M&A Trends 2024. Available at pwc.com
• Deloitte (2025), M&A Trends Report 2025 — Europe. Available at deloitte.com
• KPMG (2025), European M&A Outlook 2025. Available at kpmg.com
• Damodaran, A., NYU Stern School of Business, Valuation Multiples by Sector (updated annually). Available at pages.stern.nyu.edu/~adamodar
• INE (2024), Empresas em Portugal 2023 — Dados Definitivos. Available at ine.pt
• IAPMEI (2024), Edição PME Líder 2024. Available at iapmei.pt
• Associação das Empresas Familiares (AEF) (2024), data on family businesses in Portugal
• AFIA — Associação de Fabricantes para a Indústria Automóvel (2024), data on automotive components sector exports
• AIMMAP — Associação dos Industriais Metalúrgicos, Metalomecânicos e Afins de Portugal (2024), data on the metalworking sector
• APDC — Associação Portuguesa para o Desenvolvimento das Comunicações (2024), Directório TIC 2024-2025
• APCRI / ISCTE (2025), Impacto do Capital de Risco em Portugal 2025
• Agência para o Desenvolvimento e Coesão (2026), Portugal 2030 execution data