Buying a refurbished iMac?

I'm considering selling my 21.5" iMac (Late 2009) and buying a refurbished Late 2012 21.5" for $1099. Given the $200 savings by getting it refurbished, and that my iMac is going for about $550 on eBay, I can get a significant upgrade for only about $550. Have you had any experience about buying refurbished or selling a computer on eBay? Is there someplace else I should sell it where I can get more money for it? Thanks for your help.