Great Website, I think though that Steem should have something like fiduciary accounts, so that both parties can rest assured that the other party also has something to loose. Only if both parties agree that the trade was fullfilled as intended they would get their collateral back. I think Steem is already multisig-capable...

I went into detail here in this post: https://steemit.com/steem/@mexbit/steemit-ebay-the-next-killer-extension-for-steemit