I try to avoid the gun auction sites, because they end up costing me money.
Typically, if I look at them, I see something I think is under priced.
I have bought through auction sites in the past, and I've had no problems regarding things being fairly described, etc.
The trick is, figure out what something's worth to YOU, and stick with that- there are a bunch of guns that get listed over and over again because the seller thinks they're made out of solid gold.