If you just purchased it, that is the value -- an arms length transaction between a motivated seller and a satisfied buyer.
I many instances I have to disagree with this statement. I have purchased many sxs at auctions in western Canada where either the bidding audience had no idea what the gun was or was worth and in other instances where no one was really interested and I practically stole the guns. For instance, since it is public record, I purchased a MacNaughton skeleton action for 1500 CAD and in its condition was worth well over 15,000USD. In another instance I bought an Ithaca 4E for 350CAD in a gun shop where the consigner and consignor had no idea a what they had. And I can produce many other examples although not quite so profound.
One always hopes to find a great deal where they can turn around and make a profit. Isn't that what gun shows are all about?