Yep, stand there and watch there every move, even if you don't get the unnecessary extra's they profit handsomely from. The oil change isn't how they make money, it's called a loss leader.
My son did a job today where he actually gave the guy a part at cost, and the labor free because he knew the guy couldn’t afford it. There are a lot of really honest people out there, though they don’t get credit.
He does get infuriated by the “12.95” oil change bit. He says the only reason they charge that is to get the people in and find something big to charge them for.
The other thing that makes him crazy is people who don’t change their oil or stuff like timing belts and then come in and cry when they wreck their car.
I don’t typically stand and watch the service in progress but I will check the parts afterwards - though I did once live in a small town and the mechanic there did let me watch and he taught me alot.