I think it's the customer's responsibility to know whether the person directly in front of them is being paid, or relying on the customer to pay. If you go into a strip club in whatever country you are in, do you expect to get a lap dance without tipping the girl? Because she's in the union or being paid by the strip club? Probably not. In some states in America, like New York, waiters are basically like strippers. If you go there, you should understand that the service costs extra. You wouldn't go into a Buddhist temple in Thailand and not leave some change at the door. You wouldn't go climb Mt Everest and not give a few dollars to the sherpa who carried your bag. So don't go to a restaurant in New York City and screw the wait staff. Budget it into your travels. This is a plain rule for traveling anywhere.