I would advise doing a bit of homework, my mother in law bought herself the ladybird book of the car when she started driving just so she would know what the various bits and pieces were called and what they all did.

Then once you know a little bit, feign ignorance and just ask nicely if they can "have a look at X when it is in as you are worried about it" They ought to be able to tell you if something is developing into a problem and give an estimate for repair. If it becomes obvious that they are giving you a load of bull***t then find another garage.

A service always used to be a visual inspection as you go through each part of the service,and as long as they are honest about possible problems tell the customer and report on service sheet,its then up to the customer as to whether they want the job done

I would think most still work that way??