Second Nathan's post. KEH is a good place to buy from. Not the cheapest, but they're really honest about stuff. I got a lot of my old film cameras from them. I remember getting a Nikon 8008 from them that was listed as 'good' (a backup for my F4s) There was something wrong with it, so I sent it back and they sent me one that was completely mint in box. I dunno about selling to them.
I wish I could find a site that has used high end digital backs for sale.