We are actually developing a marketplace to help with cell phone fraud. We currently allow users to accept payments via paypal, google checkout, or amazon payments and expect to introduce Stripe Connect payments in 2013. This is only a start to preventing fraud but we have more features still being tested including a feedback system that we hope will work better than eBay's does. This thread is very helpful in determining what people want in a peer to peer marketplace.

Our site is still very new but we are open to criticism. cellsolo dot com