Professional GMing?

So, a couple of friends of mine are opening a game shop within the next couple of weeks, and, among other things, they are hosting a meeting room for ttrpgs. Now, I’ve DMed for these guys for a couple of years, and we have a good relationship. Something they suggested was that they would like to advertise me as a freelance game runner, which is flattering, but also a little odd. I am a teacher, so this might be a fun way to make a little extra cash over the summer if people were actually interested in it, but I have no idea what would go into running games professionally. How I could start to do this. I thought it would be worthwhile to pick the community’s collective brain.

PS: I mostly run Pathfinder, Dungeons and Dragons 3.5 and 5e, and Vampire the Masquerade, but I have a little experience with Monster Hearts, and have a passing familiarity with Traveller, GURPS, Pendragon and Shadowdark.