There must be. Otherwise manufacturers will insist people buying something new every year.
Not in this country. But if you feel I'm wrong, feel free to post up a link to the regulation concerned...
I was looking for a private copy. If they did an official copy, I wouldn't complain. But, they swept it clean as if their lunch money depends on it. Freely available manuals would, in fact, generate more profit. They could sell spares for far more than they could sell as part of a car.
Have you tried asking them? Most car manufacturers will sell you a handbook (unless it's a really old car) and for exactly the reasons you state - they can charge you for it.
I don't need credentials because I don't need to sell people magic beans.
You'd probably get more for them than you would selling your engineering insight!
Some shops make it a point that they only do MOT. I will go find me one of those. I might even revisit many places I have used before. I find after a few years with a place, they start getting ideas of extras. They'd go: pssst, want some magic beans, or maybe a potion of injector cleaner?
Good luck! Personally, I have a good relationship with the garage about 3 miles from me, so I can chuck my bike in the boot and leave the car with them for the day. When you have a good relationship, you can trust them not to try to sell you anything you don't need. In fact, I've never bought anything from them, except MOT tests. Some injector cleaners do actually work, by the way. I know this, and I can tell the difference between them and magic beans. Maybe, in time, you will work out the difference too?
That's my choice. But, a shop hasn't and shouldn't have this choice. They should do what they advertised, nothing more and nothing less. Tightening the sump plug with an impact gun or breaker bar is definitely not the right way. I mentioned the golden gap for contrast.
Which, at present, we only have your word for. Frankly, I don't believe you. But then, I think I probably have more experience in these matters than you do. Have you ever tried tightening a sump plug up with an impact gun, by the way?
That's the benefit of doing DIY. You can do whatever you want, so long as you have a feel for things. Otherwise, it's all a mystery.
You can also do whatever you want, even if you don't know your ar5e from your elbow. It's been demonstrated on here a few times, in fact...