Agreed, there is zero chance that Apple is doing any deep background checks on these Authorized Service Providers and all their employees.

In fact chances are, most third-party repair shops are going to end up finding such an employee who's prepared to authorize a bunch of additional repairs for a little extra cash on the side.

You're committing the most common sin of thinking-about-security: considering possibilities without adding the weight of probabilities.

If I'm going to be targeted by state actors then I wouldn't fix my computers anyway, I'd have professionals worry with that. For example, if I was an important worker for another state, the hope is that the state that employed me would take care of it. Re probabilities, the probability that a random hacker who wants to tinker will be targeted by a state actor is nilch.