Personally, I get upset when a tip is included on my bill and don't leave a penny more, even if I had intended to. I am a fairly good tipper. If I get good service, you get a good tip -- I have left up to 25% before. BUT, for a restaurant to tell me I have to tip makes me
and leaves a sour taste in my mouth. Part of it stems from a very bad night at a restuannt with sub par food, awful service and a huge bill, with of course, the tip added. I had planned on leaving 10% because that was all I felt she deserved, if even that. To be forced to pay more really got my hide.
Tipping is supposed to be a "gratitude" and earned. Not a given just "because"