It is POSSIBLE to transfer the ESP with the car to the new owner, but most often this is not done. The ESP only belongs to an individual owner and not the car. In most cases, an owner who sells the car calls up FORD and has the balance refunded rather than transfering ownership since it rarely fetches the same amount as the refund from Ford. There is also a fee associated with transfering it I think.
Watch out!
offer him 11000 and call him in a couple of weeks. i promise you, he will still have it. 