Selling a car under finance.

[BENT_8]

So my Eldest daughter has come to her senses and plans to follow in her older Brothers footsteps and build a house.
problem is, her car repayment takes up a large chunk of her income which could otherwise be redirected to deposit and mortgage.
She bought the car, a MY20 Kia Cerato, new in August last year with a 7k deposit, she currently owes 16.5k.
The finance is with St George, she's found a buyer who we've explained in full the situation and given him a no obligation opportunity to decide if he wants to go through the process and do some homework on how its safely processed or pay an extra 4k for the same car through a yard.

Has anyone had any experience in doing this, obviously we want him to feel safe in handing over his money so would like it transferred straight to St George to clear the title, although i know this will take a couple of days to finalise.
The balance of the purchase price in cash to my Daughter.

He banks with bankSA which i believe are linked to St George.

She's also been offered an instant sale to a Dealership for slightly less which is obviously an easier process but we feel if all parties are satisfied the extra legwork is worth the extra sale price.

Any thoughts.