MyBB Community Forums

I want to add a shop to my forum where members can buy and sell their Amy Winehouse items (like Amazon or Ebay) but I can't find anything that allows the members to sell their stuff too. All I can find are shops that only allow the owner of the shop to sell things, and that isn't what I'm looking for.

Does anyone know of any shops that work on a forum? Or is anyone considering making this as a plugin/mod?

Please let me know.
Thanks.