Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Paid cash for a car, but dealer wants to change price
As mhoran_psprep and others have already said, it sounds like the sale is concluded and your son has no obligation to return the car or pay a dime more. The only case in which your son should consider returning the car is if it works in his favor--for example, if he is able to secure a similar bargain on a different car and the current dealer buys the current car back from your son at a loss. If the dealer wants to buy the car back, your son should first get them to agree to cover any fees already incurred by your son. After that, he should negotiate that the dealer split the remaining difference with him. Suppose the dealership gave a $3000 discount, and your son paid $1000 in title transfer, registration, and any other fees such as a cashier's check or tax, if applicable. The remaining difference is $2000. Your son should get half that.  In this scenario, the dealer only loses half as much money, and your son gains $1000 for his trouble.