In my experience, trying to trade guns like trying to trade vehicles is always a losing proposition for ME.
The seller (be it car dealer or gun dealer) wants to get retail price for his gun/vehicle and wants to give me WHOLESALE price for my gun/vehicle so he can make a profit on BOTH items.
I have always come out better by selling my item and having CASH in hand to purchase the new item.
Now if someone advertises $550 cash or $750 trade, they are simply trying to raise their "cash" price up to retail level while the cash price is below retail.
Guess I should also add the same 'trade rules' have also held up during 30 years of being in the horse business.