There are two lines of work in the USA, which (in order to operate) don't require a state issued license.
Two industries where prices aren't regulated or determined by the market but rather set arbitrarily by the parties involved. Both businesses are so remarkably similar in nature that at times it's hard to tell one from the other.
The first profession is Art, the second one is called Prostitution.
Comment by Mary Apikos: But both are mediated by dealers and trafficers/pimps. Both involve people in power relationships in which one person usually gets fucked.