I think you're right. The big problem is all the cash jobs and they don't account for hours or efficiency on each job. There are a couple of good ones, but you're right there is no rhyme or reason to how the client is charged.
I have an offshore powerboat and guy that was doing overhaul drives, wanted me to sign a blank job card. I wrote on that job card till my hand hurt and then negotiated the terms on the bottom of page. Later tried to charge me 20k. My response, who authorised the additional cost? Not me read the contract.