"How to get away with being bad at your job" doesn't really go with "service edition", though. Because if you are bad at your job in a tipping system, you don't get paid. That's the agreement. These servers "got away with it" because they were lucky enough to have you guys at their table (case 1: understanding, case 2: tip a flat 20% regardless). You can't assume that they "got away with it" with other tables/patrons. They only thing they got away with was that they avoided confrontation over their service (we assume).