is a authorised apple repair dealer allowed to charge labor and materials to close the iMac after opening it?

If you are under AppleCare and you didn't physically damage your Mac yourself the entire repair should be covered. Call Apple if you are still under AppleCare.

In my dealings with Apple and Apple authorized service providers, I have learned that - according to the Apple rep - an authorized service provider has the option of charging a different amount or not to participate in certain programs if they wish. Case in point: my iPhone qualified for the reduced/set amount battery replacement and I was given two options: either go to an Apple store (35 miles away) or an authorized service provider (2 miles away) who had opted not to partake in that program and was charging the regular price for a battery replacement. So, I would say that it is your choice to go wherever you prefer, but be aware that you may have to incur a charge from an authorized provider.

FYI, Apple charges the service provider for the adhesive strips even for a warranty repair. For some reason Apple insists on providing them in multiple packs instead of individually. Of course an Apple Store doesn't need to worry about this as they are Apple, but independent repair centers don't have this luxury.

I will just say this : Many assumptions are based on a false premise.

Hi, Mr. Patch !

Are AASPs allowed to charge for diagnostics? In certain cases yes.

Can they charge for materials? Yes.

AppleCare Plus covers the parts and labor for a covered repair. If this was not a repair, yes the AASP could charge for the things you mention. My question is : why would you begrudge anyone making enough profit to keep the doors open? Yes, those adhesive strips cost money, and so does keeping the lights on and the doors open. You really have to ask yourself : do I wish that to be so in the future? If so, then just be grateful that AASP was there in your moment of need.

Good luck !