The place I take my car now is great, but I have definitely had some similar experiences before. Several years ago, one of my tires was punctured by a bolt. I didn't notice until the tire developed a slow leak, which abruptly turned into a big leak when the bolt fell out a few days later. My dad is super knowledgeable about car maintenance, and had inspected it and said it would be safe to go ahead and patch it. He sent me off to the auto repair shop to pick up what he would need to do the job.
When I got there and explained the issue, one of the mechanics went out to take a look at my tire. After a couple minutes, he came back inside and told me that the leak was in an entirely different area from where it actually was. He also said I would not only need to replace the tire because it was unsafe to drive on, but that I'd actually need four new tires since the tread would be uneven if I only got one. He of course recommended the most expensive ones available, which would have amounted to roughly half the value of my 10 year old car.
At this point, my bullshit detector started alarming. He wasn't hearing anything I was trying to tell him, so I just rolled my eyes at the dude and walked out. I told my dad what had happened, and later that evening he calmly called up the shop and told them pretty much an identical story as what I had tried to explain earlier. And, wouldn't you know, the mechanic told him to swing on by and he'd have the patching materials at the desk for him to pick up!