Waitresses, pizza delivery people and others do not make minimum wage. It is assumed that the difference will be made up in tips. The idea of a tip was "to insure proper (maybe prompt) service--tips. In cases where I get mediocre service, I give a minimal tip, 15 percent before taxes. If the service is exceptional, they get close to 20 percent. When I was employed and staged several banquets and meetings, I gave 20 to 25 percent--depending part on hotel policy and the attitude of the workers. I tip my barber (hair stylist) $2. They get paid on commission.
Being dependent upon tips is certainly not an ideal way to live. However, it does encourage good work habits, especially among younger workers. Technically, tips are supposed to be reported as income and therefore, taxable. I do not believe all tips get reported. There was a young waiter at a restaurant we often visit. He had made some personal mistakes in his younger days, but had gotten his act together and did an outstanding job and we believed he was going to be successful, when he moved back to his home state. We slipped him a little extra on the way out.
If the service is terrible, the order is wrong or the attitude is bad, I leave a dollar.