Don't know about PI licenses, but a realtor license would be pretty trivial. Depends on the state, of course, but in ours all you have to do is sit through boring class, pass an easy test, and consent to be affiliated with a broker, which in my case started throwing themselves at me within a day of passing the test. (After two years of being affiliated with someone else, you can take more boring classes, another easy test, and bingo, you're a broker yourself.) No background checking required.