Offer your thoughts or opinion on the input financial query or topic using your financial background.

Paid cash for a car, but dealer wants to change price
If the discount is only for financed car then their software application should have accepted the payment (electronic transfer ID) from financed bank. In this case the bank should have given the payment on behalf of your son. I believe the dealer know in advance about the paper work and deal they were doing with your son. Financing a car is a big process between dealer and bank.