What about authorized drivers?That doesn't work if the seller has another Tesla in their account. As even them moving it to a different account that they own triggers a change of ownership where Tesla removes features. (People have found this out the hard way when they wanted to re-arrange how they managed their Tesla accounts and they lost non-transferrable FUSC when they moved it from one of their personal accounts to another one.)
Then there is the issue that @KArnold brought up, is Tesla will sometimes verify that the person bringing it in for service matches what their records show. What if you have to call Tesla to remotely unlock your car, are you going to claim to be the other person?
Before transferring ownership to me, I had a service call. I was an authorized driver, and they didn't bat an eye at the service center.