Ok i don't think that RAF would be able to host the selling of these things, but Richard might be able to make a subboard somewhere, and people could post links to what they are selling there (with the links pointing to the site hosting the item, like eBay or Kijiji, etc.), becuase you're right, we don't wanna hold the Admin/staff responsible if anything bad happens. The subject could be the item they are trying to sell, such as "Animorphs Game Boy Color Game - $25.00" or something like that, and the body could be the description or even a direct copy of the Ad itself..
I'm not saying that I endorse the creating of a RAFbidding place, or whatever you wanna call it, but i'm just trying to help you figure out how to make it possible.
Hope this helped.