Auction site's actual sale records can be good,.... but, I made a living off of auctions, in my twenties, and learned that prices are almost always effected by the mind set of the seller and buyer. AKA, motivated seller, or, motivated buyer.
I use Buds Guns site. They seem to be the lowest price on the internet, so I don't get all flustered when I see the same piece for more, somewhere else. I use it as a base price for NEW pieces,... because, I always know I can get it at that price from them. Of course, transfer fee and taxes (sometimes) need to be realized, as well.