I bought from vendors that had good ratings, feedback etc. These COs are not just some guy selling his old lamp, they are professionals. I did get one server that was a little beat, but it was advertised as such. Most give accurate descriptions of equipment condition.
Can?t say this for all items auctioned, as I have only bought higher ticket items. Looking in the off brand, or cheaper equipment may turn different results, but I will continue to use these sources, even after my budget picks back up.
Another warning to keep in mind is that the buyer needs to know what he is after. The seller provides no engineering help. This could be a pitfall for less experienced admins.