Customs work does not end at the gate. The post-clearance audit is the examination of an importer's records after the goods have physically moved, checking that the duty, valuation and classification applied at clearance still hold when the full books are reviewed side by side. The audit picks the selected trader and walks the record: every import declaration across the period versus the supplier contracts, the bank payments, the sales and the stocks. Discrepancies discovered here carry the same penalties as the ones found at the border, but they affect many shipments at once, because one systematic under-declaration runs through months of cleared cargo. The protection is a standing file. Importers who archive every declaration, the corresponding invoices, transfer documents and payment records line by line, enter the audit with an answer for its questions. Those who trade without the archive face reconstruction under pressure, where memory substitutes for evidence. The audit is not a punishment; it is the routine backstop of the entire system, and the only reliable response is a record so current that the auditor's questions answer themselves.