But isn't that the point?
You're paying a "professional" to do a professional job. You shouldn't need to say anything about what to do/use/consider etc.
What happens if you have no knowledge or understanding of the "intricacies" of what they are doing or, more importantly, are supposed to be doing - such as wrapping felt around heating pipes?
That's their job - it's their profession - That's (partly) why you're paying them lots of £££'s to do the job.
How many professional mechanics know the true attention to detail required to change the belts on a V6 and for them to be perfect until the next change is due?