What is it you are looking to have done?
Unless its special machining, a lot of “gun smithing” is knowing how to swap and/or polishing parts.
A couple of decades ago I paid for a trigger job on my 1911’s. A few years ago I took a 1911 armorer’s class and learned the bulk of a trigger job consists of replacing a single spring.
I’m not looking for anything in particular. I know someone who claims to be one. I am highly suspicious. I have seen him at shoots and his weapons malfunction. He had a Charles Daly (it didn’t even function) and I don’t know of anyone who thinks much of those particularly one who can build a nice weapon. Another shotgun would not cycle. He claims to have a bunch of Glocks in to test for a law enforcement agency. I am unaware of weapons having to be “tested” after purchase. It is not as though they are fitted with anything. I would assume they would be tested at the factory or by the officer receiving the weapon. IN the Marine Corps we got new weapons packed in grease. We cleaned them and used them. No testing. Of course we sighted in. But what do I know.