How can Customs tell if an Item is counterfeit?

Question

For example; a louis vuitton purse.
?

Answer 1

They are given information from the manufacturer or owner of the name brand. It points out certain markings and things to look for when checking.

Answer 2

An average customs agent would not be able to tell definitely if a designer item was counterfiet. They would be able to put together clues however. Did you buy it in a foriegn country? How much did you pay for it? When "designer" stuff is sold cheap, there is a pretty good chance that it is couterfeit.