It's simple.

You give the suggested donation or more to the artist's charity of choice, you get the offered item.
Posting access is moderated, at least for now. I would love a co-moderator.
And yes, this can be for anyone offering things for any charity. Want to sell a pendant for Planned Parenthood? Didgeridoo for Doctors Without Borders? Whatever.
It just seemed like there was sufficient interest, and I'd love to see this take off.