now a performer does a good evening,an American Tourist,who is used to tipping,pays his entrance fee,and decides at the end of the evening to give an extra[not abunch of fives].
what does the performer do,refuse the tip,explain that its not the done thing and upset the tourist,or accept it.

I understood that the Americans referred to had not paid an entry fee, but the price of the drinks was inflated to cover your fee, unbeknown to them. Either way, it would be bad manners to turn down a gratuity from anyone for whom it is culturally normal or anyone simply wishing to extend a compliment in that manner. Turning drinks down (politely) is a different matter as one can always think of a logical excuse not to drink any more - hopefully. Having said that, I sincerely hope that tipping doesn't become any more widespread than it already is in the UK.