Which document is crucial for proving the legality of goods in customs?

The customs declaration is a vital document in the customs process because it provides comprehensive information about the goods being imported or exported. This document typically includes details such as the nature, quantity, value, and origin of the goods, which are essential for customs authorities to assess compliance with legal requirements.

When goods cross international borders, customs officials rely on the declaration to ensure that the appropriate tariffs and taxes are applied, that the goods meet safety and regulatory standards, and that they do not violate any laws or trade agreements. The customs declaration serves as a formal statement made by the importer or exporter, attesting to the legitimacy of the goods and their adherence to relevant regulations.

While the other documents listed may support various aspects of the transaction, such as the bill of lading representing the carriage of goods, the purchase order detailing the buyer's intent to buy, and the commercial invoice outlining the sale terms, they do not comprehensively confirm the legality of the goods in the way the customs declaration does. Therefore, the customs declaration is the principal document proving the legality of goods in customs proceedings.