I have spent time on both sides of the table at gun shows, I have also spent time in the car business. One thing that I found in both places is that the person wishing to trade most often values their property much higher than it's actual worth. Yesterday while visiting with a friend at a gun show I witnessed a young man come in with a Sako, 22-250 bolt with a Nikon 3x9 scope. He asked my friend if he were interested in buying the gun, my friend took a look, then handed it to me since I favor Sakos. I immediately graded the gun at about 85%, the stock had numerous scratches and dings, there was some bluing wear on the floor plate and trigger guard as well as some slight rust on the end of the barrel. My friend asked him what he was asking for the gun, the guy popped off, "I know it is worth at least $1200." I assessed the gun value to be in the neighborhood of 5-6 hundred at most, and that was being liberal. My friend didn't even make an offer after hearing the response from the guy. Several hours later I saw him leave the show carrying the gun.
I seen the same thing happen in the car business numerous times. I remember a guy telling me how good his trade in was trying to jack up the appraisal I had given (offered) on trade, I finally told him, the car you are trying to trade is better than the one you are attempting to buy, since it is so good, why don't you just keep it? We didn't trade.
The first thing one needs to do if they are anticipating trading, it to examine the gun and do an accurate assessment of the condition and grade it accordingly, then go to a reference (Blue Book of Gun Values) and find an approximate value of the gun. Keep in mind, just because you paid 5 hundred for the gun two years ago does not necessarily give it a value near that today, it could be worth more, but most often it will be valued at 75 percent or less of the actual purchase value not including the tax/transfer fees.