I've never really had a big issue with any gun I've bought online, from a store, or from an auction site like GB. I doubt it's luck at this point, as I've bought about 35 used guns over the last 14+ years on GB and other online auction sites. Not a stinker in the bunch.
I've bought guns from both Classic and Aim Surplus and have nothing bad to say about either of them. The Beretta 81 I got from Classic a few months ago is in great shape, and yes I paid extra for a pretty pick, but I've bought other guns from them without the pick option, and when they said "good to VG", they meant it, and that's what I got. Actually, I would say it's much closer to "excellent", than VG.
As far as Aim goes, every used/LE gun I've purchased from them has been better than described. The first one was a Sig P220 DAK, which was in nearly new condition, except for an odd dull spot on the muzzle. Last one was a Jericho 941F, in fair shape cosmetically, but a great shooter. I did have to hunt up a new guide rod as the one in it wasn't the correct one (it didn't fit), but a friend bought 2 of them the same time and his look just like mine, but had the correct guide rod. They only would have found the rod issue if they had taken the slide off. It was obvious something was up with it, as it was loose and wasn't even snug against the barrel. You could rack the slide fine, but firing it could have been dicey. I've bought about a half dozen other handguns from Aim, and all were as advertised.