why the Dickens shouldnt they be tipped,if the member of the audience has enjoyed the evening,and does so voluntarily. as an organiser,you can not prevent someone tipping an artist.,any more than you can stop them buying a performer a beer, or a cup of coffee or a soft drink.

Absolutely right, as long as it doesn't become expected or compulsory - but it's very unlikely..

professional folksingers are lowerpaid than catering staff

Are you sure about that?