Are all plumbers thieves? How do you know when they are taking advantage of you?

I was informed by my elderly mother that she had some plumbing work done for $1000.00...to repair a leak. The Plumber came out the first time and charged a $210.00 leak detection fee cutting 4 holes into different parts of the house. He said he detected the leak and would come back the next day. He came back and discovered the leak was not where he thought but where I was doing some remodeling work. There was no water damage in that location. I was not there to dispute it. He patch a leak and according to hime ran 12ft of new line...for $935.00 dollars?....2 hours and 15 mins worth of work?