No you are not paranoid, sadly that has been my experience of services done on other peoples cars, and why I still do my own unless it came with the price of the car, and even then I know they wont do everything. 
I do all the work on the family cars ,having not trusted work done by garages in the past ,
all the family drive vauxhalls with the exception of one ......
a 2002 picasso hdi

he insists on driving it

few weeks ago the clutch went
had a quick look to diagnose , he needed the picasso working again in a hurry ,so it was recovered to a local cluych place ,who quoted £350 ish done for next day
i took him to collect it ,
they said the gearbox casting needed replacing too due to the casting being cracked ,another 389 quid

I went outside and looked ,old casing with 16 years of dirt on it
went and asked , "not new ,reconditioned " they said , "so where is the old cracked one" i said ,
and when people recon gear boxes ,they clean them at least ,some paint them
we could not prove they did not fit a recon box or casting , so he had to pay the extra £389 to get the car back .