I understand being paranoid. But if you're handing over the key cards, you have paperwork with a legal agreement that they're purchasing they car.
Keeping the car linked to your Tesla account only exposes you to unneeded risk.
My friend recently did this, and within 2 days of handing over the car, the new buyer purchased a month of FSD beta @ $199. And it was of course billed to her.
Have fun untangling that, or any Supercharger fees that happen from the person you handed over the key cards to.