I have some sympathy with fast fit centres. It seems to me perfectly reasonable to have the technician have a look around the car while quoting or fixing the issue you took it in for. Most motorists haven't a clue and wait for the MOT for example to highlight issues.
They are after all commercial businesses out to turn a profit.
Indeed. But they prey on motorists who don't have a clue. We've all seen it. What you describe would be fair enough if they applied sensible standards (i.e. the MOT criteria) and advised customers of anything they notice that truly falls below a roadworthy standard.
What I and, I'm sure, many others on here have seen is that they'll even fail items at MOT which are perfectly OK just to make money out of motorists who don't know any better.
On several occasions Mrs. KW has been to fast fit outfits for tyres in a car that I know to be perfect in every other respect only to come back with a list of "urgent" issues. "Tracking", exhaust, brakes at least, normally. Fortunately she knows more than she lets on, and tells them to shove it, but it's clearly an attempt to exploit customers who appear not to know better.

Kevin