25 years ago, me and one of my best friends decided to become gunsmiths. I left the country for a few years, when I came home, he had done a correspondence program of some kind and become 'certified'. He was getting work through some of the pawn shops, and he gave it up after a while for a few reasons. (Now he's a chopper pilot instructor.) First of all, he said it isn't nearly as much fun to work on guns that aren't yours. Second, he said, just because you have a piece of paper that says you are a gunsmith, doesn't mean you have all the knowledge you need to do it well and be competitive. He was losing money, because he would botch jobs and have to buy things.
All knowledge is good knowledge. Even if it just gives you the background to know when you are getting bad information. But if I wanted to make a serious living as a gunsmith, I would become a machinist, and get as much experience as possible working with metal cutting tools.