How would manufacturers know when cars change hands?
The same way that every single marketing company, bank, finance and insurance company does. It's public information.
The same way that every single marketing company, bank, finance and insurance company does. It's public information.
Not all cars get registered though - some are chopped for parts (in which case that infotainment system might live on in another car), some are shipped internationally to be re-sold elsewhere, etc.
And there could be a lot of lag - some cars languish on dealer lots, get auctioned, languish on another lot, get auctioned again, etc. Or a dealer might like your car and slap dealer tags on it and keep it essentially as his personal vehicle for a while without registering it.
Lots of little opportunities for data to leak or remote functionality to be abused. There ought to be a complete, no-joke, absolutely reset everything in the car (and expire any remote access tokens) option in the car itself, that either a buyer or seller can easily invoke.