Possible plumber ripoffs?

[Zack Howard]

I recently had a plumber come out to fix a leaky pipe on the well cap. Dug the hole and everything for them so it would be a quick job. In and out in 2 hours. The plumber showed up and he had a trainee, that's fine and all. But then the bill came and it had double labor for the trainee. Is this normal? If so why not just bring the whole family and make 6x as much?