Over $50 per person it is going to have to be really good service for me to go above 15-18%. But if I go grab a cheap meal at a sit down place for lunch and the service is good. I could tip 100%.
% of total bill is useful but not end all be all. I am not going to go to Denny’s and eat $4 breakfast and only tip 80 cents because that is 20%. I am also not going to tip more than 20% at Ruth’s Chris even if the service is good because 20% of $150 is still $30 to serve two people