Excellent call out! Please add it to the guide as a note or call out at the beginning. I think that process would be worth its own guide if you ask me. Would definitely link it to this one if you do.

I thought the orange and red squares in this image represented where the listed components (the ambient light sensors, the camera module, proximity sensor, and front mic) are located. And if that’s the case, shouldn’t the warning be to separate the adhesive outside of the marked locations to help minimize the chance of damaging those components? I’m wondering why you would focus your prying efforts on the areas where there are really delicate and easily damaged parts…

There is no certification for him to just start performing repairs on out of warranty devices. If the devices are in warranty and the customer doesn't want their warranty voided then he would need one of Apple's hardware certifications. Those can only be obtained while you work for Apple or an Apple Authorized Service Provider. The only thing I might suggest if he does start his own business is that he get liability insurance.

If you live near an Apple Store or a MicroCenter they will be able to provide him with the best training for starting out. If you don't, and you've got an old iPhone or 2 and you can afford a couple of battery or screen repair kits from this website, he should be able to fumble his way through his first guide.

Apple has an entire application process for those businesses interested in becoming Apple Authorized Service Providers (AASP). This program is specifically for business who are interested in performing BOTH in warranty and out of warranty repairs. Information on the application process can be found here. If your business is more for out of warranty repairs, then you can apply to be an Independent Repair Provider which is a lot less strict and information for that program can be found here. Best of luck!

What about disconnecting the battery?

Isn’t there also a Samsung Certification?