Odds of Hanging On
If you're self-employed or working on commission, you're going to constantly be working just to hang on. If you're good at what you do and have customers, you should be fine...unless you are getting a fixed hourly rate (in which case, you're set unless your shop closes unexpectedly).
In order to ensure you keep business and people keep coming back, turning on the charm could definitely help. That, and actually being able to fix cars. The moral of the story is: Once you're in, you'll always be working on trying to stay in.