It's like Ebay except you don't pay cash/paypal except if the seller is charging you shipping, otherwise you bid w/credits you get by doing things. It's so cool. I'm on their "selling" and buying things all the time.
I enjoy Listia very much. I've been able to get rid of a lot of item I had bought to sell on Ebay that just would not sell. Ebay's fees are too much, and with Listia you can charge shipping or offer free shipping! The items with free shipping sell for a lot more. I've got a lot of great things on Listia and have always been treated fairly with customer support.