Customs Import Export on the GRAJ protocol. One fee. 195 countries. Join the protocol.
Almost every customs problem is a document problem, and almost every document problem was created weeks before the goods moved. The expensive part is not the duty — it is the container sitting at a port accruing demurrage while somebody finds a certificate that had to be arranged before departure.
Commercial invoice, packing list and bill of lading are the baseline. What holds goods is the fourth document — the one specific to the product or the destination, which cannot be produced after the fact.
Somebody must be legally responsible for the declaration in the destination country, and it is a real liability. On DDP terms it is you, which usually means registering there or appointing a fiscal representative. Sellers agree DDP to win an order and discover the registration afterwards.
Customs value has its own rules and can include freight, insurance, royalties and assists. Under-declaring — including by innocently omitting an element — is a penalty offence in most jurisdictions and is exactly what an audit looks for.
Inward processing, bonded warehousing, free zones and duty drawback are established mechanisms for goods that are re-exported or processed. They are unused far more often than they are unavailable.