I only trade or sell off guns that I have no real attachment to, that don't get shot, or that I have no real need for.
Then again, I buy guns that I don't want or need, when they present themselves at a great price, for exactly this reason....to trade or sell for a profit later.
I never sell or trade for less money than I paid or traded into it for. Guns aren't holy to me like they are to some people, so when I have one that doesn't ring my bell, I will get rid of it, and have never suffered sellers remorse.
I did sell a gun for MUCH less than I should have though. That sucked and stung a lot once i figured out what I did.
The gun would still have been sold, but for much more. Learned my lesson, and research my guns if I am unsure, and always bring the smartphone with me to gunshows to research, for this exact reason