Are tips ever absolutely *required* (if it wasn't advised as mandatory in advance)? Or can a customer simply choose to not give a tip, ever, as a matter of principle? Or can a customer refuse to give a tip, at all, after receiving (what he feels) is shoddy service?
And does it matter, at all, what type of service it is? Barber, waiter, taxi cab/car service, counselor, delivery guy, valet parking, coat room attendant, airport baggage handler, etc. What are the differences between them, if any?
And IF you do choose to tip, how much is standard?