The reality is we are at the upper echelon of owners by just being on this forum....most of us, at least. I feel for the person who knows absolutely nothing about maintenance, mechanical things, etc.
I lease most vehicles but now actually owning my truck, I really keep a close eye on services performed and things fixed by the dealer.
Yeah, I have an employee that was told a brake flush once a year was necessary and paid $900 for rear brakes on a Tahoe. You're right though, we are the upper echelon on vehicle owners. If shops weren't getting away with this a high percentage of times, they wouldn't be doing it. IMO, people on most forums probably represent less than 1% of any consumer base and we aren't who sales or service cater to.
I was at a firestone shop getting an alignment on my previous truck, a woman came in wanting an alignment and a tire rotation on her Audi AWD car. They cross rotated the tires then told her they couldn't align it because the tread depths were different on the front left from the front right and that would cause the diff to burn up.
They told her she need 4 new tires and quoted her over a $1000 then told her the car wasn't safe to drive and they couldn't "legally" release the car back to her for liability reasons; she started crying as they were full on giving her the scare treatment and gave in to their tactics.
I'm sitting there hearing this BS and told her that it was just that, BS, get your keys and leave. The service writer tells me to stay out of it and that he's right; I told her to call Audi service and when she told them the scenario, they told her they were lying to her and to leave. She ended up having to call the police to get her keys back.
Unfortunately, these people get away with mistreating a lot of vehicle owners