The HS code is the importer's problem

The first six digits are the Harmonized System, maintained by the World Customs Organization and identical in every country that uses it, which is almost all of them. Beyond six digits each territory extends the code for its own tariff and statistics: eight digits in the European Union, ten in the United States, and various lengths elsewhere.

Which means a six-digit code agreed with a seller is not a classification. It is the first two thirds of one, and the duty rate lives in the part that was not agreed.

• Underpaid duty, recoverable from the importer with interest, often years later during an audit rather than at entry.
• Penalties, which in most jurisdictions scale with whether the error is treated as negligence or something worse.
• A missed preference. A code that sits outside a trade agreement's coverage pays full duty on goods that qualified for zero.
• An unexpected trade remedy. Antidumping and countervailing scope is defined by product description and anchored to codes. A classification that lands inside a scope can carry a deposit larger than the goods.
• A licence requirement that applies to one code and not its neighbour, discovered when the entry is rejected.

The system has interpretive rules, and the most common amateur error is classifying by intended use when the structure classifies by material, function or state. The second most common is accepting the seller's domestic code, which was chosen for the seller's export statistics and may have no counterpart at your end.

Sets, kits and goods made of several materials have their own rules, and so do parts, which are sometimes classified with the machine and sometimes on their own. These are exactly the cases where a confident guess is expensive.

Most customs administrations issue advance rulings that bind them for a period: in the United States a binding ruling from the customs authority, in the European Union Binding Tariff Information, with equivalents elsewhere. You describe the product, they issue the classification, and it holds.

On a repeating programme this is the highest-return paperwork in the whole transaction. It is free or nearly free, it takes weeks rather than months, and it converts the largest open variable in the landed cost into a fixed one.

We agree the classification in writing with the buyer before the order, we state it in the landed price so the duty line can be checked, and on any product near a scope boundary or a preference threshold we recommend an advance ruling and say why. Where the seller's code differs from ours we reconcile it before the invoice is issued rather than after the container has sailed.