It only takes one unscrupulous greedy manger and the whole shop goes into ripoff mode. I know this from the experience of knowing some people who used to do this crap back in the 70s.
It used to be far more common and it was the reason people who could, worked on their own cars. Because we knew better than to take our cars to those shops who would scalp you.
Not just Sears:
Driving X country, 1 year old Chevy K2500HD, needed oil change in FL, went to Chevy dealer. They put 6 qts oil in 5 qt engine. (found out when I read the bill)
...”Service Mgr/writer”. We’ll credit you for the one qt. {had them drain and re-do]
Needed oil change (forget which state), went to WalMart (local recommended). Saw them hosing down engine compartment afterward... HEY, you’re watering down the electronics in there!
... “Service Mgr”/writer: they spilled a little, how else to get the oil off?
Went back to grovelling on the ground like a reptile and changed my own for most of my trip.