It is difficult to convince a man of something his livelihood depends on him misunderstanding.

Every professional has their peeves and once set they imagine them everywhere. I suspect part of taking your car to a second mechanic is finding one who is neutral on the exact problem you're having. I had a car fail emissions and the diagnosis was a new set of injectors for a good fraction of the value of the vehicle. My fiancee got a recommendation from a coworker for a shop near our apartment. Replaced some worn EGR hoses for $200 and I passed with flying colors. Same shop talked me out of another repair I thought I needed. Kept going to that guy for several years after we moved to the opposite end of town.