ruralcarrier said:
I would most likely leave a few $$ (5%) IF service was deserving. Otherwise I would move on. I have found asking anyone, unless you know them pretty well or you are recognized as a repeat customer, is only an invitation for more confusion or rhetoric to extort more $$. I didn't have anything to do with making French laws or customs so I feel it is best to follow what you know to be the norm.

One long gone French restaurant owner, Bruno (not the same owner of Dreams) who owned La Petite Auberge des Iles in Marigot, is the only one I have asked that has been 100% up front with me. I don't make it a habit of asking but after many repeated trips there and discussions with Bruno, he would shoot straight with you.

If service is above average at a Dutch side restaurant we often leave another 5% there, even with 15% added on. I have also found even asking on the Dutch side has pitfalls also. Some servers will imply the 15% is only a partial service charge as 3-5% of it goes for the Turn Over Tax or to the restaurant itself. It may or it may not but that is not my problem to deal with when there is an added 15% service charge.