this is true. I was thinkin same model ebay uses. Have the auction site, but have payment through a paypal like clearing house that uses bitcoin. And keep fees managable for sales, none of this crazy percentage crap those guys are charging. I was thinking ~1-3% Fees Btc on selling. Maximum.
Just thinking randomly but with bitcoin, it might be an idea to have sellers put funds in escrow to be refunded after the sale is complete and you take a percentage of that. Of course, that means that sellers must have funds in the first place...