What would cause me to sell a gun?????? MY WIFE says that if I want to add to my collection, I have to sell something.
Just wait until she runs out of ideas to buy me for my birthday, anniversary, Christmas, etc. LOL
When my wife got pregnant with our daughter in our younger 20s, she told me to look inside the gun safe and to sell everything I haven't shot in 6 months as likely, I won't shoot them in the next 6 months.
She also asked me to sell our Kawasaki 250 and Yamaha 125 dirt bikes along with dune buggy and project classic car as I need to focus on raising our daughter. And chances are, we would be replacing the dirt bikes with quads to ride as a "family" and replacing 2 seater dune buggy/classic car with 4x4s that will accommodate the entire family of 4 (They were replaced with Yamaha quads, 4x4 truck, 4x4 suburban and C5 Z06).
While I vehemently disagreed with my wife (Letting go of some of the guns like NHM-91/P226, which I hadn't shot in 6 months not because I didn't like shooting them but I was "saving" them and shot SLR-95/Glocks instead) but in the end, I gave in to her "nesting" and sold off most of the gun safe content and all of the dirt bikes/dune buggy/classic car.
After our son/daughter were old enough to ride their own quads with "family friendly" suburban for me and Super Lifted 3/4 ton Chevy truck with 454 v8 and 35" tires for wife, when we were riding in the desert and shooting up the canyons, she told me she regretted "making me" sell off the guns as she realized how much I enjoyed shooting (I had been shooting USPSA matches for some years by then).
Wife and I agreed on a new contract. She won't question what guns I buy to restock the gun safe as long as she gets to spend double what I spent on my hobbies ... NO QUESTIONS ASKED.
So from time to time, wife would even suggest, "You haven't gone shooting in a while. Is it time for you to buy a new gun?"
One Christmas in year 2014, I go on a shopping spree (I was trying to get one of 250 Dan Wesson PM7 made for CA each year but just missed out while calling my wife for final OK as it sold within the 15 minute call and she suggested I get another 1911 and ended up getting railed Sig 1911 TacPac as consolation) and ended up spending over $7000 on gun stuff. When I told my wife, she beamed and said, "Oh, so I get to spend $14,000?" with a smile. We had just bought one of two retirement properties at our retirement location and she would simply tell me to pick up this and that for the house in terms of appliances, flooring, toilets, paint, etc. along with chickens, ducks, turkeys, goats and mini pigs (She sure tried for mini cow ... but it was a definite "NO" from me as I was the one who would be cleaning up the cow manure).
In the end, it would have been better had I not sold off the content of the gun safe decades earlier and I regret having sold off most of them.
After retirement, we sat down to tally up various spending for hobbies and were mildly surprised that over $180,000 were spent for guns/ammunition/shooting accessories/reloading components with over $160,000 going to ammunition/reloading components mostly for USPSA practice/match rounds with total over a million rounds of factory ammunition/pistol and rifle reloads and 22LR. So during lifetime, cost of guns gets smaller compared to ammunition cost, especially if you shoot a lot.
Moral of story is if you have guns you like but don't shoot them much, it may be better to keep them to appreciate them later than regret having sold them. But if you can sell/trade guns that you are not shooting for guns you would like better and shoot more often, then that may be a better thing.