Gun shops go out of business because they went into business with no plan on how to competitively conduct and grow their business.
You need good business experience, lots of money; lots of product; ability to obtain financing; vision on how to grow your business; and a keen awareness of your local and internet competition.
Local shops that I've observed make it through difficult times have: 1) busy ranges and rentals; 2) offer something else like paintball and airsoft games; 3) work the gun shows on a large scale and professionally; 4) have a sporting clays range in their "back yard"; have large inventories.
I'm sure there are other factors like offering training and classes, etc. But, whatever it is, they aren't just some guy with a big gun collection who thinks he can turn his hobby into a business.