It was years back, I had to move like three times in one year and each time I had a problem getting my internet set up; so I lost more and more clients each move.
It was fun though....mostly. I completely tailored my games to the client but laid it down that once the game started I was the final arbiter; otherwise they'd ultimately feel like they were wasting their money. Most games were awesome. I had a long running Pathfinder game about a pair of bandits stumbling ass backwards into becoming the mayor and sheriff of the very town they'd been pillaging that ended up being so awesome that I'd float them sessions weeks they couldn't afford to order and even invited them to unrelated games. I hated losing contact with them the most.
I had another solo game where the guy wanted to play Call of Cthulhu from the perspective of the monsters. It was a weird power fantasy that I never really enjoyed; but he got a kick out of it. I had one group that were full of swingers and that extended to the characters; that was uncomfortable but they paid on time so I rolled with it.
90% of my business came from groups trying to figure out how to get started on their own (that I'd usually sneak some PDFs to help them out later) or GMs wanting help learning a new system. Just seeing the parts they were struggling with in play as many times as they wanted and being able to ask the little niggling questions that the book doesn't think to answer helps tremendously.
Occasionally I'd even custom design a campaign for another DM to run. I actually did one for a groom to run for his own bachelor party one time; which makes it one of my favorite jobs because I love telling people that my fat, hairy ass was entertainment at a bachelor party once.
I was also approached by a fairly well known Sci-Fi author about designing a system for her setting. She already had character sheets printed out and wanted me to the fit the mechanics to what she had...which was a bunch of gibberish that someone that had never actually played might come up with. The printable character sheet was 8 PAGES long and included details like Birth Sex: Gender: Preferred Pronouns: etc...that contributed nothing mechanically and would just make printing it a bitch right next to important stats like Strength and Intelligence. So we argued about that and eventually went our own ways; the low-ball offer she made me to design the thing wasn't enough to have my name be associated with the abomination she was envisioning.
Taking into consideration the amount of time I spent planning the games and how much I charged ($5 per person, per 2 hour segment; plus tips which were actually where most of my money came from) I probably made minimum wage; but it was something I would have been doing for free anyway, so I feel like it was a damned good deal while it lasted.