Practically speaking, however, they are liable for the time to service those customers and diagnose product issues to determine that the customer was at fault. And, that extends to any future buyers of used devices. And, any resulting displeasure from customers, even though it wasn't Apple's fault.

These sorts of things are exactly the types of problems that exist in the used car market, for exactly the same reasons.

Yep. That’s why I think Apple tends to lock down their spare parts.