I got into automotive work for that reason exactly. Problem is, there is always someone cheaper. By inflating prices, you can charge more, while appearing to charge less to the layman. I have never done it. I always had people ship parts to me. But I could see with a large operation how when you scale it you would earn more business with a profit margin that is easier to maintain.

Thats why I switched to doing things other people cant or wont do and charging whatever I want. Way easier.

I would personally rather pay the actual hrs it took. Some vehicles could be pretty rusty underneath so that would definitely cost more. And I can understand the charging double on parts since if it fails the shop has to eat the repair.