When I had my shop I did a fair amount of gunsmithing. There were local shops but none of them did repairs, or they were so backed up or over priced that I got a good bit of work over three years, and still have some people bring me their guns. Since I don't have a license now what I can do is somewhat restricted (no overnight keepers, receiver modifications, etc).
You do have to have an FFL for gunsmithing, which is an expense and paperwork hassle, as you have to keep a bound book.
I thought it'd be interesting, but in my experience, it wasn't what I was expecting.
Quite a few "My shotguns don't cycle" (clean it once in a blue moon mmmmkay?!), "my AR15 jams all the time" (clean it once in a blue moon, mmmkay?!), etc.
Mostly cleaning. There were a few times I had to hit a lathe, and more than once I had to custom make some parts I couldn't find. (Remington pump action 22 with a snapped firing pin, I fabbed a new one from scratch). Reworked a few AR15 uppers.
One example I remember which turned in to a real pain in the butt, was an AK74 pattern rifle - customer said it would fire one shot, that's it. I was skeptical as AK's are reliable creatures by default. Century had bubbasmithed the receiver together. The magazine latch and front trunion catch ledge weren't lined up. Ended up custom building a new magazine catch / trigger guard assembly from scratch and making a set of 4 modified magazines that ran clean through it.
But mostly, it's a lot of cleaning, replacing springs, cleaning, cleaning, "can you mount my scope with a bore site?", "can you put night sights on my handgun", and a lot more cleaning.
I never considered myself a "true gun smith", just got pressed in to it as a byproduct of the shop. It gets you on an intimate level with firearms, which is nice.
For awhile.
I consider true "smiths" the ones who have been doing it for a long time, who have enough parallel experience that they can take a weapon they haven't seen before and
"figure it all out".
Rare are the real smiths, who can cover everything from refinishing, replacing parts, rebarrelling actions, fabricating parts, etc.
More often you'll find people fall in to a specialization - this guy is good at refinishing, this guy knows how to tune revolvers, another guy who knows how to chamber and true bolt guns, this other guy is great at 1911's, or Garands, etc.