I promised to report back - the 'old' Model 3 is transferred to it's new owners (current give me the vin). Mostly painless process though I would suggest not selecting a Friday afternoon as drop off time because the car needs to be inspected before the transaction can complete so I had an (unnecessarily) anxious weekend with the car at receiving waiting.
The transaction is now complete though and I would recommend these folks to anyone needing to sell a car w/minimal pain.