Actually, when customs officers have doubts about an item that might be counterfeit, they can keep it until a brand representative states about it.
if it's obvious, they just seize the item and you'll have to pay a fee to close the file and stop pursuits. The amount of the fee depends of the item, quantity, purpose (personal use or resale), its value and if you are a first timer. You can refuse to pay but then you go on trial.
Two years ago, I ordered gen A&F clothes from A&F original website. The parcel was seized and delayed for 3 months before being cleared. I called several times to know what was going on, they were always saying the items were going under verification.
Finally, I got a phone call asking me to come to customs department as officers had to ask me some questions. They were suspicious because A&F clothes labels were saying they were made in several countries, so they sent one of my tee to the brand representative in France, then in the USA to know if they were gen or not!
After 3 months, nobody was able to confirm they were gen (and they were as I ordered them on the website!!!) and they finally released the parcel. I spent 2 hours there, and had to explain why I did order clothes in the USA, why there was different sizes, and so on...
Sp guys be careful and don't mess with French customs, they can really annoy you...
---
I am here: http://maps.google.com/maps?ll=43.382103,-1.654883