Where can I find that value of rifles? Auctioneer is pulling the wool over me!

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I am having an auction, and liquidating many of my late husbands rifles. The auctioneer traded me part cost of the advertising for a 30 caliber carbine for his daughter. He gave me $300 for it and said that it didn't retail for more than $185 in the books. Later on that day I found the receipt, and we paid $300 plus tax about 6 years ago! I know rifles increase in value..especially if they are in prestine condition, so I think that I might have made the wrong decision. Now he wants to know if I would like to trade another in exchange for 1 or 2 % of his commission. I quickly said no...but I would like to find out how much these things are worth. ANy ideas?