There are genuine sellers on clubsnap (2nd hand market) where I have gotten my first DSLR, and a few lenses from.
Most of the users there know the market rates well and aren't willing to pay for higher prices , hence the lower prices listed there (just my personal observation).
Condition wise, I think most of them are not exactly the same as stated (by the forum's guidelines). For instance, my last 2 lenses bought on CS was rated at 10, which is supposedly rated as lightly use. However, the lenses had minor scratches or signs of use on the exterior, which I personally would not rate as a condition 10 lens. Nonetheless, I am not that fussy about the condition and it's up to you how much you're willing to tolerate for used products.
