Side gig to earn profit.
Not me, I do it for fun.
The legal test will be did you earn a profit from the sale of firearms and did you buy them and then sell them for said profits.
It’s one thing to have a collection of firearms and sell a few. Although I would never sell a firearm each and every one is a lifetime possession. It is entirely another to buy a group of weapons and then sell them at a mark up which is by definition for profit. I am sure people will try to get around the new law and the alphabet boys with unlimited legal funds and unlimited swat teams worth of mouth breathers will start nabbing those people and making them spend thousands in legal fees and bail. The process is the punishment in most cases. The other way is if you intend to sell firearms for profit just do it legally and get a FFL it’s not hard to get and it allows you to have mail order guns at will and turn a nice side gig doing transfers for $35 each worth 10 min of your time.