Even if Apple has room for improvement here, I think it’s still worth it to try to curb the market for stolen parts, because that’s going to exist even if Apple

Even if Apple has room for improvement here, I think it’s still worth it to try to curb the market for stolen parts, because that’s going to exist even if Apple sold spare parts in bulk at-cost simply because there exist unscrupulous repair shops that have no qualms with charging you OEM part prices while using gray market parts that cost a fraction as much on eBay, Aliexpress, etc. For instance, maybe Apple could supply parts in bulk to repair shops but require registration of those parts prior to usage. The repaired iPhone would function regardless but loudly alert the user that unregistered parts were used to repair it. Gray market parts naturally aren’t going to be able to be registered (either due to serial not existing in their system or having been parted out from stolen devices), and thus the user is given some level of assurance that they’re not paid for questionable repair services.