When on the Dutch side, if they don't have an extra fee added I usually add 20%. If they have a 10-15%, then I just give them that and that's what they get, unless I really liked the service, then I can add more if I want to. If they wouldn't add the charge I am a good tipper, (if I get decent service).
We don't eat a lot on the French side but have decided this time we are going to eat many more meals over there. So, what everyone is saying is that the fee is already added and I don't have to to tip, but if I really like the service I can add some more if I so choose. This sounds fair enough for me.
Really, it sounds like the French and Dutch sides are the same at most places. They just do it a little differently is all.