If you want to make money at detailing, go high-end. Cars that cost $80k and up. Sports cars and SUV's. These guys want it done right (= spotless! no dust anywhere on the interior!) and will pay good money to have it done right.
A good place to look for customers is those who are selling cars. Either high-end dealers or individuals. The dealers probably already have someone, but they are ALWAYS on the lookout for someone else--who knows when their current guy is going to flake out? Move out of town/raise prices/start doing sloppy work/get a job doing something else, you name it.