The key is good service and doing the jobs properly.
A customer must have confidence in what the gunsmith is doing for him.
I once took an old rifle to a 'gunsmith' to have him make a replacement leaf spring for me. He just gave me a blank stare. He didn't have a clue what to do.
Another, actually told to me by the 'gunsmith' who did it, put a very high dollar English double shotgun into a hot blueing tank separating the barrels. He reduced the value of that shotgun from about $50,000.00 to $50.00.