Some (genuine/real) experiences as a seller:
...there's a scratch in the varnished finish of the 97 year old gun you sent me so I want half my money back....
....the head space of this 1909 Lee Enfield SMLE MkIII passes the military gauges but I handload and it's not good enough for me so I'm sending it back...
Horror stories of unrealistic buyers and sellers, (and trades are a whole new mess) is the knife that cuts both ways.
As a seller, often the buyer actually has limited knowledge of what he's actually buying and asks the wrong questions...Then is unhappy when he actually has the item in his hands.
As a semi knowledgeable buyer, buying is always a craps shoot as usually the seller doesn't actually know what he's selling, and the fact that it belonged to your grandpa does not automatically make it worth more money to me, and does not make your 10% condition gun a 90% condition gun...except in your mind.
In my view it's always a trade off, sometimes it's cash, other times it's goods.
I've done trades where both parties were extremely pleased, and others where both were marginally cheesed.
The mark of a good trade should be that both parties have the same reaction, if only 1 side is happy that's a bad trade. If both sides are unhappy, it was probably a fair trade, but both sides probably thought they were putting something over on the other...
Just as a side note, it's amazing how often "sanded and refinished" is interpreted as "new and unissued"...
Been burnt by that several times ;-(