Nice looking bike
LeBonCoin is a happy hunting ground for myself and @woodbutchmaster
. Like all sites it has a number of chancers and the odd faudster, (that is a story for another day) but there is a lot of good stuff on it, obviously French, but also Italian, some Spanish, German, depending on the border region. And of course if you are looking for French components, or French threaded stuff, (like Campagnolo pedals) it has a wide choice.
It can, however, be very frustrating: there is a habit of not removing old adds, sellers tend to over use key words (so the number of adds for actual Merciers, for example, is far below the initial number shown in the search), sellers can be very arbitrary as to accepting bids, the secure purchase option that an increasing number of sellers use only works with a French credit card and the postage can be complicated if you are outside France (as I am).
The postage costs referred to in the ads are always for mainland France so you have to get an individual quote and that is if the seller is interested in packing the item, and the bigger it is the more reluctant they are. Plus, since the start of the year posting from the EU to the UK has become more difficult for one off individual sellers, filling in the Customs form requires, exact weight, correct customs code, and a range of other details that make many people think it is not worth the bother.