As a person who frequently buys antiques, for myself and when people ask me to negotiate I usually…read morehated the US shops whom gouge you on price. These people have excellent quality objects and they are quite flexible on price, which as someone who is a student and intermediary for other people in their purchases, a very good quality.
You might like to brush up on vocabulary in French to try working a deal with them, and try reading some antique books to know good prices or how to lower an offer, I have both on my side, and I also didn't try english with them. Even with my muttering in english they never commented or spoke english if that is an indicator to you guys.
These people have quite a fabulous selection and I'm gratified to be a customer of theirs I shall be patronising them for quite some time.