So now a car is not really a car any more
The sale and transfer of a car is now likely to involve the manufacturer regardless of private or dealer transaction.
It's not really like any other tech, as I don't need to engage a third party I may have had no relationship with to clear and sell my phone.
Your personal data, along with the car's data is now spread out across your phone, internally within the car, and with the manufacturer. Just deleting your app (unlikely) or, resetting your car (even less likely) is not sufficient. The car does not change it's credentials on transfer either, VIN number stays the same for the life of the car. Where does this lead? Confusion over data being mine and personal, data that is car specific for the manufacturer and a vast, Ill considered gulf of grey between as current discussion shows. Overall modern cars are not "yours alone" like cars used to be before they gained SMART (oxymoron alert).
Relying on the seller to de-register is pointless and may be unfeasible if they are not alive, abroad, incapacitated, phone stolen or account closed etc. This is simply unworkable.
There needs to be some new broader thinking about how we now effectively borrow cars from the manufacturer regardless of the process we went through to get the keys...