Working as a caddie at an exclusive golf course way back when, we had a couple of golfers we called "Mac n' Duff". Where as a normal tip for 18 holes might have been up to five bucks, these two could only make 9 holes fortuately and would give you 50 cents. That and I had older sisters working in the diners as did I but only as a dishwasher.
I know how hard these folks worked or at least most of them so I give at least 20%. The places I frequent know me so they attend to us quite well.
For those that regularly do not tip even 15% for good service, maybe you should eat at home. I say that for the obvious but also because if you get to be known as a cheapskate, you won't ever get good service.
I will add that not only will I tip accordingly for bad service but will let the head honcho what's in charge know.