Ok Mr NB23, since you seem to be pedantic and need it all spelled out, here is what I do: When the time comes for a service I take my car to the garage, give them the keys and say "I want an oil service/inspection 1/major service/whatever-terminology-your-car-manufacturer-uses". Then the garage knows what I asked and they go and do it. The car comes with a little book, the book inside lists the jobs that have to be done, oil service at x miles, brake fluid at 2 years, transmission at x miles, greasing this at this interval and all those wonderful things. I then expect the garage to do the work, I pay them and all good.
Now, you seem to say that I cannot possibly trust them to do the work. Well ok but certain things require an amount of trust or we would never get anything done in this life. It is also why people sometimes take their business elsewhere as they are not happy with the results. I trust my garage, they do seem to do the work I ask of them.
Same with a CLA. I take it to the guy, say a CLA. That means I want it Cleaned, Lubricated and Adjusted. So the guy knows what needs doing. I trust him to do it because I've seen the results. I have also used once somebody who I now do not trust at all. That is not a reason to never service the camera, it was a reason to find the guy I trust.
I hope that is clear enough for you. Have a nice day and we're still waiting to hear if service your car or not? Do tell us and also do tell us what you specifically tell the garage over what I have described above. Or you know, may don't. I'll just block you. Shame, you'll never see this.