I run a similar "hobby business" - at least that's what I call it. I've posted about it before on here; I refurbish and resell old electronics, mostly laptop computers.

As of today, I've sold more than 800 machines at an average of $80 per machine and an average profit of $30 (approximately). That's around $24,000 of profit over the last three years or so. It covers all the costs of its own inventory, parts, losses (e. g. some machines just never make it to sale), and it's built a lot of fun community relationships. Plus, I've helped a lot of people get access to a working computer at a low cost!

This would never, ever scale beyond me doing it. The moment I had to employ a person, pay rent on a space, or start offering warranties and free returns and so on, that profit margin would vanish. That's why it's a hobby, not a full-time job. I do it on nights, weekends, and in between working my day job (e. g. I'll have a Windows install going in the background while I code).

But it's fun, it's valuable, I've learned a lot about running a business, and it's paid my car payment a few times. It's also nice to have a 'job' that is very different from my day job: much more hands on, not as much complex thinking required, and more immediately rewarding. (At least for me. I just love when a broken thing starts to work again.) The hardest part is the customers, especially when things don't go well (e. g. are my fault) or they are in a bad mood.

I think more people should do things like this. It doesn't have to be the thing that gives you the money you live on to be valuable.