I think that if you have a dozen guns, and every once in a while you sell or trade one off to get a different one that you want more, you are ok. Different if you do this on a regular basis and deal in a hundred guns a year.
Just my 2 cents, but most people do get tired of guns cars and anything else, and at some point their tastes change, I don't consider that being in business. If you go on FL guntrader, that's what you will see,"for the most part" but there are guys who are selling a dozen guns, "I would think that is probablly illegal". But I have traded a gun here and there, maybe one or two times a year, "usually to step up to a better model", "or a change in interest". I don't think that is a problem
Also if someone offers you double what the gun is worth and they can legally own a gun, why not sell it to them. I had that happen several times, just by changing grips and sights on a stock gun. If someone offers me the right price, everything is for sale.
A guy wanted a 45, and I had one he liked, he traded me for a gun that cost double so I traded him. As it turned out he was doing a trade with his brother and needed 2, 45's to trade for a shotgun his brother had, and he liked mine, he told me this after we had met and done the deal, but he was a ccw holder, "not that he had to be" so I ended up with a better gun, he ended up with a shotgun he wanted. Many people don't know what their gun is worth or it's not important to them, so why let it get away.Also some of us have been buying guns for 40 or more years, and things just change, like revolvers, when I started shooting everyone had a revolver,1971, now I have no revolvers.
I think the law is made for people "as mentioned several times" who make a living doing this or even a second source of income, not the occasional shooter who decides he wants a different gun.
Some guys are never happy, and sell every gun they buy after a few months, those are the ones I like to run into, it's like cars, let the first guy take the beating.