The governing documents of the enterprise, the share register, any shareholders' or operating agreement dealing with voting and appointments, the manager's employment agreement and any delegation of authority. Together they should show who decides what.
Write the control down before anyone has to prove it
Small businesses often run on understandings, and understandings cannot be filed. When the enterprise is formed or purchased, take the opportunity to record the arrangement properly: the ownership percentages, the voting rights, who appoints and removes the manager, which decisions are reserved to the owner, and what spending authority the manager has. That is ordinary good practice for any business with an absentee element, and it also produces exactly the evidence this question needs.
Keep the manager's employment agreement consistent with it. A file in which the owner claims direction and the manager's contract grants full autonomy answers the question against itself. Where a business is bought rather than formed, ask whether the constitutional documents can be amended at closing, since that is the only convenient moment to do it.
Hypothetical example: Vinh is acquiring a U.S. studio that restores antique clocks. The first document review should make a funds trail from the earliest lawful source through every transfer to the business account, then pair it with ownership papers, a lease, invoices and an operating plan.
Bank statements alone rarely explain the whole chain; sale agreements, tax filings or gift records may close the missing links. Gather records in chronological order before preparing explanations. Files become difficult when money moves before the writer knows which document proves each transfer, or when an invoice is paid without showing why the purchase is connected to a real operating enterprise.