Auction site for trading unwanted items

I have just become aware of a no cash auction site.  You earn credits by "selling" unwanted items and can use the credits to buy things you want.  Sounds like a nice idea.  There are free credits to get you started at sign up.  You can check it out at www.Listia.com.   I think I will find out more about it and see if it can help me get rid of some unwanted items.