Side money doing DIY question NOT SPAM

hello - I have been doing a few projects on the side for some extra pocket money. Commissioned furniture, general repairs and carpentry. Not enough to make a living but enough to do things like pay for vacation and gas money, etc. I do projects like decks or kitchens or baths or whatever roofing, etc. Most of my work has been word of mouth. My prices reflect that my availability is limited by my day job. I do quality work and usually have something in the pipeline.
I have been in contact with a national company selling products that need installation. They are fine working with part time local installers for their products. The project is simple to install and may also have some add on work possibilities that go 100% to me. Their fee schedule for their installs seems a bit low to me but not bad if I can do the installs quick. Anyway, that's not the gist of my question.
My questions have to do with licensing, permits, etc. The state I am in does not license general contractors. Each township has its own requirements for license requirements, what's required for a permit and so forth. I do have a "license" with the state to collect sales tax, etc.
How does a contractor claimed to be licensed? You see that all the time. In my state I'm sure guys, even the bigger ones, are not getting licensed in each township they operate in. What a logistical nightmare that would be. Even just knowing for each township what requires and what doesn't require a permit is a real PIA. Some townships around here require plumbers, electricians, etc. to be licensed. Others do not specifically mention it although I suspect they do to. I'm in a gray area as a generalist. What to do?
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