This website involved listing pictures of items and allowing users to comment on the items. Login method will be my facebook or twitter.. and ebay api, amazon api, will be integrated into the website.
There will be ability to deposit money much like how getafreelancer has it.. you deposit for credit in your account. There will also be arbitration fee if necessary.
The backend should have an ability to set an amount of money to take from
1) Closing cost
2) Opening Cost
3) Arbitration fee
More details will be posted to your message if interested in bidding.