Starting a business is quite the expensive endeavor in our modern times where everyone want to sue everyone for everything. I have been sued for an employee getting one tire off a residential driveway and damaging the grass to the point they called a grass and tree surgeon....nope not kidding. Grin!
How it works locally is that many insurance companies provide Business Liability Insurance be it an electrician, greasy spoon, carpenter, gun shop, or small retail, etc and etc. They provide liability insurance that is more or less blanketed to provide against public liability claims. The catch is that even as a sole proprietor before you can obtain state and city or county business license you must obtain and pay for workers compensation. This does not protect you the owner at all, however it is required to open any business regardless of employees or not.
Yep, everyone has their hands out. It takes quite the sum to grease all the palms. You may eventually find that you will be charged more expensive riders due to the shop is related to guns, regardless of air or powder. Check with a couple local agents and ask about typical business insurance and if it will cover what you wish as they would be the correct route locally.
Cheers
Kit