An expert witness is a specialist appointed either by the parties or by a court or tribunal to provide technical opinions on matters requiring specialised knowledge — financial valuation, accounting, engineering, medicine. In financial disputes arising from M&A transactions — warranty claims, earn-out disputes, valuation disagreements — the financial expert witness prepares a detailed report presenting their methodology, assumptions and conclusions. In common law proceedings, expert witnesses testify under cross-examination; in civil law and arbitration contexts, their written reports carry primary evidential weight.

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Example: in an ICC arbitration between a French buyer and a Swiss seller over a CHF 4.5 million warranty claim, each party appoints a financial expert witness. The tribunal-appointed expert is charged with resolving the methodological disagreement between the two party experts on the normalised EBITDA calculation. Hectelion's expert witness report demonstrates a CHF 380,000 restatement error in the buyer's calculation — a finding that reduces the claim by CHF 3.0 million after applying the agreed multiple.

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Hectelion experts serve as expert witnesses in international arbitration and judicial proceedings on financial valuation and M&A dispute matters.