Oh man, what you are dealing with here is a moron. This person is trying as hard as possible to get out of paying for these import fees. My suggestion when anyone anywhere has an import fee issue is to create a post on the BL forum, make it very on point and act like you are not sure why they need to pay. Once the people start responding and likely flaming your buyer a bit for not understanding customs import fees and their own country, point them to the discussion. Make sure you are 100% on the side of the buyer in the post and other people will do the dirty work for you and some of them will be people who live in France.
Unfortunately in this type of situation you have to educate the buyer in the laws of their own country and that is best handled by a group of people not just 1 person. Someone will take the advise or knowledge of a group much better than an individual.
Good luck, hopefully this doesn't stay a lose/lose situation for you.