I would definitely avoid websites like that... You could also try amazon for used equipment. They often will have something used from time to time...
If the site looks shady, it probably is. Hardwareking apparently has 5970's in stock. I call BS on all of it.
By the way, are you looking for 5830's, 50's or 70's? Or just an even distribution of the three?
It all depends on the price per mhash. Ill probably going with 5830's due to the price but would certainly prefer 50's or 70's if I can find a deal. Found some 5850's for 140 shipped but by the time I grabbed my card and got back to the computer they were sold out. Im really not comfortable buying used equipment for this type of project so no ebay for me.