Tell him to look at the "completed auctions" rather than the ongoing auctions. The sold auctions without the "R" (reserve) that have bids, are what guns have actually sold for. Looking at auctions with the "R" that have bids, would give him a good idea of what price people are willing to pay, even if they don't meet the reserve.

He would have to register at GunBroker, to see the completed auctions, if he is not already registered there. The reason you don't pay attention to the ongoing auctions, is that the price listed may be WAY too high, and will not get any bids. Or if they have bids, people wait until the last minute to put their bid in, so the price would change at the last minute.