If you're an honest importer, you already know more than you want to about the U.S. Customs Service. You know about paying duties. You know about filling out your customs entry form. But do you know what an assist is? Do you know how to incorporate royalties, license fees and buyer's commissions into your customs paperwork? If you don't, you should, says Gerald McManus, vice president of regulatory affairs for forwarder and customs broker BDP International Inc. of Philadelphia.

McManus, formerly assistant commissioner for commercial operations at Customs, explained the rules in understandable, edifying and painful detail at a seminar on regulatory compliance sponsored by BDP.

Importers may want to take heed - especially as U.S. Customs, using increasingly sophisticated methods, works to ensure compliance with import laws.

Here were some of McManus's key points:

At every importing company, "somebody has to take responsibility" for complying with Customs regulations, "or it's not going to get done," McManus warned. Then, Customs may attack the company with fines, penalties or a stiff regime of cargo inspections. "Work under the assumption that you're going to be audited" by Customs, McManus said.

List Commissions. Importers often forget to list commissions on their customs paperwork, and it may haunt them later. An importer may pay an overseas agent a commission for finding suppliers. These commissions must be listed.

The commission can be deducted from the dutiable value of the goods, "but you have to have a written, binding agreement" with the agent, McManus said.

Another often-overlooked item is assists. Assists are materials or services supplied by the buyer, free or at a discount, to the suppliers to help produce the needed item. Let's say you import film projectors from Japan, but you have the lens made in the United States and shipped to Japan for incorporation into the final product. Instead of reporting the projector's value at $100, you would have to report, say, $111: that's $100 for the projector, $10 for the value of the lens, and $1 for shipping the lens. "You can probably classify the lens as free of duty," because it's U.S.-made, "but you must declare it," McManus said. That's a duty-free assist. There are also dutiable assists.

Let's say you shift production of the projectors from the United States to Indonesia. You send the tools for production from here to there. You must declare the tools as assists, report their value in accordance with Generally Accepted Accounting Principles, and pay duties on them. The value must include shipping cost.

An air conditioner sent to the plant in Indonesia to make the workers comfortable is not an assist, because it is not used to produce the goods, McManus said.

License Fees. Royalties and license fees must also be reported to Customs. These are fees paid to a foreign supplier for such things as distribution rights or exclusivity agreements. "That is dutiable. It's added to transaction value" on the customs entry form, McManus said. If the fees are paid periodically, such as quarterly, they must be allocated to each separate entry.

Customs auditors "will find these things in the snap of a finger," McManus warned. However, "if you're paying the fee to a third party, even one that's here in the U.S., it gets very questionable" whether it is dutiable, he said.

It's best to seek professional help for these situations, he advised. But the rule of thumb is this: If you can get the goods into the United States without paying the fees, then they're not dutiable.

For instance, if you import caps with Olympics logos from China, he explained, you must pay the Olympic Commission a licensing fee. But the fee isn't dutiable, because you can import the goods without paying it. Only the actual distribution, not the importation, entails the fee. One thing importers sometimes forget to report to Customs, and which can cause trouble, is related-party transactions.

If you import goods from a company related to yours, you must report the relationship to Customs. Companies are related if either the importer or exporter owns more than 5 percent of the other company's voting stock, or if there are blood relationships between the owners, he said. Another item to consider is the fact that sometimes the price of an imported good can change after the importation, for various reasons, such as a transaction agreement that accounts for changes in currency values.

Failing to report the final transaction value, if it is different from the one reported to customs, can mean big trouble, McManus said. It's best to alert Customs to the potential change and ask it to withhold liquidation - that is, delay final acceptance of the entry paperwork.

Companies should issue written procedures, and train their employees, to make sure all these Customs regulations, and others, are followed, McManus said. "Don't sweep anything under the rug."

After all that is taken care of, he said, companies can go to the next step - structuring their transactions, and taking advantage of special programs, to legally minimize their du-ties.

But it's better not to take such steps without addressing the more basic issues, he warned, because you may attract some unwanted attention from Customs.