A good friend of mine who recently passed away told me about purchasing his first car, brand new, using money he made from repairing TVs around his neighborhood. He started by running tubes to the local store, testing them, and replacing them. Then, he bought a tube tester and a small stock, which he'd carry in a wagon.
There was a doctor in his neighborhood with the first model of a color TV, and the tubes would constantly overheat and pop. This was the cash cow that bought him his first car. He eventually realized that he could solve this issue by adding some active cooling to the TV by running a small fan off of one of the TV's circuits. And that's how he accidentally killed his first job.