Here ya go: https://www.jalopnik.com/tesla-remotely-removes-autopilot-features-from-customer-1841472617/
Edit: Ah, sold privately, as in directly between individuals? I'm not sure about that, but they totally could. They can track the location of the car; if it starts getting parked at a different house regularly, for example, it'd be easy to tell it'd been sold.
I'm always a little shocked when people ask me if my product is on Amazon. I never even considered it because I've known what they are for so long; it's been a bit of a wakeup call that most people still have no idea how fucking awful Amazon is. It sucks struggling with market visibility, selling just from my own website, but it beats the hell out of being bullied like this until I'm big enough to have my product stolen and copied by Amazon Basics.