When I was a kid in Brooklyn, there was an Earl Scheib nearby. Their method was to spray the wheels without masking, then paint the tires black with a brush.
It stands to reason that if you're painting 20-30 cars a day, you should be pretty good at spraying because of all that practice. As others have said, the key to a decent paint job is proper prep work. I've seen a number of very nice Earl Scheib paint jobs applied over well-done bodywork. You wouldn't have known Earl did them. Mindset is important, too.....if you're expecting a $5000. paint job from one of these places, you're only kidding yourself.
FWIW, I just saw the Maaco 'Winter Special' ad...their Ambassador job for $199.