There's loads of authorized apple retailers and apple repair stores, even in countries which don't have any official Apple Stores. So there must be a certification program for those.
I'm not sure if the grandparent was getting to this, but sharing your client information with a 3rd party in the EU and/or for EU citizens is problematic w.r.t GDPR. You'd have to disclose to your client that you are sharing their data, why you are sharing, and get their informed consent.
Consent is only one legal basis, but it’d be hard to argue that sharing their data for processing by Apple is legitimate interest, and the other non-consent bases don’t apply here.
No worries here, Apple IRP actually requires independent business to get a waiver signed by the customer. Among other things Customer acknowledges repair has no warranty from Apple, despite repair being performed "using original Apple parts by Apple Certified technician working within Apple authorized independent repair program"!
Why Apple should know that a random Joe replaced the touchscreen of his iPhone?
I don't see any reason. HP doesn't know I replaced my keyboard three months ago and the keyboard works.