Why don't people want to pay artists?

It always confuses me why people think that face painters will work for free. I have bills to pay, kit to replace and children to feed. I understand charities can not afford to pay out lots of expenses but they can charge a decent fee to split between the artist and the charity instead if only wanting to charge £1! They could also look for a sponsor!

I don't mind donating my time for causes close to my heart. But I value my profession.