To find gun values I like the instant downloads available from gun digest. They're only a couple bucks, which is nothing when you're buying and selling guns. As a serious gun collector, I can see two GLARING PROBLEMS with trying to infer values from online gun auctions: 1) Its fine for a common gun where you see multiple examples for sale all the time (like a Remington Model 700 for instance), but if you want gun values for less common or rare guns you might not find a large enough sample size in the auctions to ascertain the value of your gun based on its condition. 2) You don't get factual information critical to determining value - things like history, number of guns manufactured (to determine rarity), and gun values based on condition. The online auction only describes the gun for sale, and perhaps gives a "Buy it Now" price, but you have no way of knowing how the seller arrived at that price.
However, if you're informed going in, you can tell whether you're being ripped off and/or if the seller is full of baloney on his/her prices. Here are the
Gun Values downloads I'm talking about.