What should be done with the money remaining after the death of a buyer who paid more than the value of the item and did not receive the change?

If the deceased is the debtor, the debt is to be paid from his estate, and the creditor may absolve him of it. If the deceased is the creditor, then the debtor must repay the debt to the heirs of the deceased. If he does not find them or cannot reach them, he should give the amount of the debt as charity on their behalf. If he does find them, he should give them the choice between upholding the charity or receiving their due.