What is Customs Valuation?

Legal Definition
Customs valuation is the process where customs authorities assign a monetary value to a good or service for the purposes of import or export. Generally, authorities engage in this process as a means of protecting tariff concessions, collecting revenue for the governing authority, implementing trade policy, and protecting public health and safety. Customs duties, and the need for customs valuation, have existed for thousands of years among different cultures, with evidence of their use in the Roman Empire, the Han Dynasty and the Indian sub-continent. The first recorded customs tariff was from 136 in Palmyra, an oasis city in the Syrian desert. Beginning near the end of the 20th century, the procedures used throughout most of the world for customs valuation were codified in the Agreement on Implementation of Article VII of the General Agreement on Tariffs and Trade (GATT) 1994.
-- Wikipedia