c. Effect of Good Faith of the Payee

Responsibility of One Who Accepts an Undue Payment of a Thing Certain and Determinate in Good Faith

He who in good faith accepts an undue payment of a thing certain and determinate shall only be responsible for the impairment or loss of the same or its accessories and accessions insofar as he has thereby been benefited. If he has alienated it, he shall return the price or assign the action to collect the sum. (Art. 2160, Civil Code)

For example, A, believing that he was obliged to give B a house, delivered it to B, although A did not owe B the house. B likewise believed that the house was due to him. B was in good faith. On November 1996, the house was rented in the amount of P2,000 per hour by a movie producer for a particular motion picture and, while shooting, the kitchen was accidentally burned. After the shooting of the motion picture, B was paid the rent in the amount of P30,000 for 15 hours on December 1996, A discovered that he did not owe B the house and demanded its return. B, having received the house in good faith, is responsible for the impairment of the kitchen only insofar as he benefited from that impairment; the rent alone does not establish such a benefit.

Reimbursement for Improvements and Expenses Incurred by One who Unduly Received the Thing in Good Faith

He shall be exempt from the obligation to restore who, believing in good faith that the payment was being made of a legitimate and subsisting claim, destroyed the document, or allowed the action to prescribe, or gave up the pledges, or cancelled the guaranties for his right. He who paid unduly may proceed only against the true debtor or the guarantors with regard to whom the action is still effective. (Art. 2162, NCC)

Rules on payment by an incapacitated person

As a general rule, payment by one who does not have the free disposition of the thing due or capacity to alienate it is not valid. This means that the thing paid can be recovered.

Art. 1427 retains its original wording but has no present application to minors between eighteen and twenty-one years of age because the age of majority is now 18 (RA 6809, Sec. 1). It provides that when a minor between eighteen and twenty-one years of age who has entered into a contract without the consent of the parent or guardian, voluntarily pays a sum of money or delivers a fungible thing in fulfillment of the obligation, there shall be no right to recover the same from the obligee who has spent or consumed it in good faith.

I believe the above provision is no longer applicable since the current age of majority is 18.