I think the use case is clear - the problem is real and your proposed solution sounds good.

There is obviously a lot of room for misuse, but the same was true for E-bay and yet they were able to overcome this by offering such a large value proposition for users to risk it and by internal measures.

For people who really want to improve, the value should be there. Maybe you can copy some of E-Bay's best practices to help keep your user's in-line.

I wouldn't use it though - I'm perfect ;-)