I've lived in the US all my life and am still confused about when tips are expected and part of the wage structure. Sit-down restaurants with an assigned waiter are the easy part, it's all the other cases that quickly become confusing.

It's not helped by the fact that every order-at-the-counter restaurant now asks for tips as you pay. It's almost to the point where I assume that a tip is needed if and only if I'm not asked for one. No wonder it's confusing to visitors.