Garage Attendant: You fellas have nothing to worry about. I'm a professional.
Cameron: A professional what?
--Ferris Bueller's Day Off
I'd say anyone who takes pay for Tarot reading is a professional. Whether that's their main source of income or not doesn't really matter in my book.
I used to do the psychic fair thing before a lot of cities started cracking down on business licenses. I should probably get one, though I'm not sure if I need it for my city of residence or one for each city I want to read in, etc. That's the problem of living in a major metro area with a bunch of satellite cities. They all have different laws covering the same things and it can get confusing.
So instead, I read for friends. Sometimes they give me cash, but more often they'll buy me dinner, drinks, etc. It's an excuse to see them, really, and everyone goes home happy.
If you do want to read for John Q. Public, be warned--most of your clients will be good ones. However, you'll get Crazy, Stupid, Arrogant, and everything in between, too. And some days you'll swear that the Universe cannot possibly make enough alcohol so that you can deal with some of these clients. Seriously. :/
Good luck with whatever you decide to do.