A lot of clubs run their singer's nights, just so they can defray the cost of paying a good guest. In case they don't take enough money on the door that night, to cover his/her/their fee.
In common with many folk club organisers, I have paid less than I took on the door on a given night, to that evenings' guest.
Only one performer has come to me and said, "You haven't taken much tonight, don't feel you need to pay me the full amount".
Well I paid him the full amount, as that's what i agreed, and he has a living to make. This was some 30 years ago, and that guy is still singing today, a lovely bloke, and a great entertainer.