In a time when the local residential and light commercial "mom and pops" were charging $55/hr and almost no parts markup to bring in and keep business, I calculated a 10% profit margin (most industries would consider this austerity) for my one man shop at $137/hr with no parts markup and paying myself about $20/hr! I'm sure I could have made it work with the customer base and my quality of work / reputation, but growing a business where the first question out of the customer's mouth is "what's your labor rate?" would have severely limited the situation. I decided not to open the doors as a result.
An employee / tech making $20/hr costs the employer $45-50/hr with the expenses on average. Add in the overhead and support employees, van, fuel, parts stock, licensing, taxes and everything else that keeps the doors open, and it's easy to see why our industry doesn't run the 30-40% profit margins of some other industries in the US.