Well Don, I do a lot of charity work myself, but I would not dream of asking perfect strangers to give their services for free.

Thing that tends to piss them off is the Bar is usually normal prices, yet the licencee is never asked to donate his profits to the charity, the people providing the venue rarely do it for sod all, same with caterers etc, its just the poor bloody band who are expected to perform for nothing, yet if they refuse, or even just ask for expenses, they are considered tight gits.

Way of the world I suppose.