I do not know this to be fact, but what I read was the following. Some users had features on their cars they did not pay for. They sold the car as legit having these features and when Tesla did an audit and removed those features the new buyer(s) was mad and thought Tesla had screwed them.
Yup... though the one very widely reported situation was actually a bit different, and showed a different internal Tesla issue.
In that case, the original owner did pay for FSD.
Then Tesla ended up buying the car back.
At which point they flagged it in their back-end systems to have FSD removed (entirely legal since they owned it again).
But, they immediately sent the car to auction... before the back end system had ACTUALLY REMOVED FSD from the car itself.
Car was sold at auction to a 3rd party dealer over the weekend (without anything in the sales papers saying it came with FSD or not)- and dealer then sold the car to someone as having FSD on it (since it was on the car when they looked at it).
Next week comes around (dealer still has car, not been picked up yet)- software audit sees back end says "remove FSD" but car has FSD, so it gets removed from car.
Dealer thinks it's just some glitch, tells customer it's just some glitch, and delivers the car to customer.
Who now has no FSD, and Tesla tells him "Yeah you didn't buy FSD"
Eventually from bad press (and the fact the fundamental confusions was caused by their back end taking too long to update the actual car) they gave it back to him for 'free'
That's highlighting how poor Teslas back-end IT is though- not highlighting a real "issue" with Teslas policy on 3rd party sales.
But like I said- make sure you get the receipts