Cliff, everyone who's ever dealt with you, including me, knows you do excellent work for a very fair and honest price and if you say that's what the job is worth, we all know you can be trusted.
The issue here though is a mechanic giving a price that the client agreed on, but then jacking the bill waaay up without checking 1st to see if the extra work and money is OK before going ahead with it.
Years ago my wife and I booked a room at a lodge for a week of snowmobiling and asked for a price for an all inclusive stay. He gave me a price that I felt was fair and agreed on it. At the end of the week we went to check out and he told me that he'd given it some thought and had decided that he wasn't charging me enough and wanted an additional $200. I refused to pay the extra and gave him the agreed on price and left.
There was about 25 of us that stayed at that lodge a few different times but after the attempted rip-off and me telling everyone about it, nobody ever went back. He tried to beat me for $200, but ended up losing a few thousand dollars in the process.