Gary Fox Plumbing and Heating Charged $800 for 30 min of work, RIPPED OFF and took advantage of old lady kent Washington

My Mother recently had loud noises in her home when water was turned on from faucets around the home, she called the water company and they had told her to contact a plumber, she was nervous about this as she has been taken advantage of by plumbers before and not understanding costs. She contacted Gary Fox plumbing and they came over to take a look, gentleman was extremely friendly and assured her she needed a new valve and its a fairly easy fix that doesn't take to much time at all. The next day he contacted her and told her it would be $800, she was taken back as he said it was an easy non time consuming fix, but what can she do? She has to have it fixed, the plumber came over and sure enough he was correct, it took 30 min to fix, he insisted he pay her cash and he will deduct $50 off the bill, He left no receipt. When I came home i asked her how everything had went and she said it cost her $800, i asked how long was he here and she said 30 min, on their website they charge between $150-$175 an hour for labor, i contaced Gary and asked him some basic questions, he told me he charged her $300 for the part, which I found on the internet for $200 but understandably they have to markup their price, so I said how did we get to $800 then? Are you saying you charged her $500 for 30 min of labor? He stuttered for a second and said "Well thats just what it cost, and your Mother was fine paying it" I said thats not the point you took advantage of an elderly lady who has no idea what shes doing, with an $800 bill your saying the part is $300 that means you charged her $500 for 30 min of work, how dare you? He then hung up on me with no explanation, I called other plumbing companies and they said it should have been a $300-$400 job and they were sorry of what had happend, Stay away from these blood sucking thieves!!