My opinions on this is the same with unpaid internship. F off. Is it charity? if not no. Do I even know you? If not no.
9 times out of 10 its just gonna encourage the person into thinking they can get shit for free, making them a pain to other artist and devaluing labor.
All your gonna get is becoming known as the go to guy for free shit. Ie "why do I have to pay you while X would do it for free"