Kevin Carey tells a tale:
While Congress has become pretty thoroughly professionalized in recent decades, state legislatures are still home to some genuinely eccentric people. Back when I was working for the Indiana General Assembly, one member (and not the member who was, no lie, a radio psychic) became convinced that it was crucially important for the state to address, via statute, the problem of rogue hypnotists travelling the land, preying upon unsuspecting Hoosiers. He wasn't anti-hypnotist, mind you–he thought the government needed to protect people from unqualified hypnotists. If you ask me, real hypnotists are the ones we should be worried about (You want…to give me…your credit card…information…) but then I'm not a duly-elected public servant.
So the state passed a hypnotist licensing law, complete with the requisite boards, professional standards, forms to fill out, fees to pay, and so on. The law is still on the books; see here for more information on the Indiana Hypnotist Committee and its approved study guides (e.g. Hypnosis, Is it For You?, Lewis R. Wolberg, M.D., Dembner Books 1982.) If you're interested, the next exam is scheduled for Friday, December 11th at 9:00 AM. Bring a pencil!
Then, after the law was enacted, a funny thing started happening: The state began receiving license applications from people who didn't live in Indiana. People who lived in states (i.e. most states) that didn't require hypnotist licensing of any kind. Some were from as far away as California. It turns out they were doing it so they could advertise in the yellow pages and on bus-stop billboards as "state-licensed." They would just neglect to mention which state.
Carey's point is that (a) there's a lot of stupid occupational licensing laws out there, but (b) there's also a need for some way to signal that you're competent. I would add two more lessons: (c) people aren't always honest about the signals they're sending, and (d) sometimes licensing can facilitate that dishonesty rather than restrain it.