Reputation is key.
Work with ranges. Even a $25.00 gun cleaning job helps.
If you keep a customer's firearm for more than 24 hours, I would suggest getting a FFL. Also, some parts dealers give discounts if you have a FFL.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)