You don't need a storefront, but you do need a legal place of business. The place of business can be your home, but when the ATF agent comes out to verify your place of business he's going to be expecting to see a business license issued by your local government. Not all localities permit home-based retail businesses. You'll have to check local zoning ordinances and regulations.
If your locality doesn't allow home-based business, you can always apply for a special-use permit. But in these anti-gun, politically correct times, getting a locality to issue a special-use permit to run a home-based gun business is going to be a serious uphill battle.
Also, if you don't sell enough guns annually to demonstrate that it's a legit gun business, the ATF won't renew your FFL when it comes up for renewal. The ATF has been cracking down on home-based FFL's for the past decade and trying to put as many as possible out of business. The days of getting an FFL just to buy cheap guns for yourself and your buddies is over.
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