I owned a SMALL shop for 9 years.I had a separate building at my home --3 acres in the country--and ,for a while,also sold live bait and some fishing stuff.(State owned lake a few hundred yards form the shop) I had to jump through hoops and hire a lawyer to get approval from the zoning board.
At the time we (wife and I) belonged to several gun clubs and had a fair customer base going in.We also worked (yes,it IS work) a helluva bunch of gunshows...HUNDREDS.
It is IMPOSSIBLE to compete with guys who have a HUGE inventory,bought at distributor prices and ,basically,selling at what it COSTS you to buy it or even less..Your best chance to make a few buxs is too TRADE and make a bit from each deal.But you'd better know what you're doing or you can lose money pretty quick.
By the time you do all the paperwork---Fed,state and local taxes,sales tax,log book---AND pay for insurance,utilities and all...you'll be fortunate to make minimum wage.
Would I do it again?? hhmmmmm ..........................................yeah,probably.
Good luck!!