Customs authorities can audit past import declarations, sometimes years after the goods have already been sold, comparing your declared values and classifications against market data and other importers' declarations for similar goods. Penalties for a genuine error are usually less severe than for a pattern suggesting deliberate evasion, which is one more reason accurate, well-documented declarations from the start matter more than any single shipment's outcome.
If you receive an audit notice or a valuation dispute, respond promptly, provide the documentation you have kept, and consider professional advice for anything beyond a straightforward clarification; ignoring an audit notice rarely makes the situation better.