Running has judges. Just the other day in the women's 1500m (I think) a woman was initially disqualified for pushing someone. She appealed and the decision was reversed. It's all about interpretation and subjectivity.
I can't think of any sport that doesn't have a judge or referee that has to subjectively interpret athlete's actions and the sport's rules.
Not American so perhaps I'm missing something, but doesn't it make sense tips are taxed? It's income, so why wouldn't it be?