Question

Scenario: John, a businessman, owns a small store in a local market. He has been following a certain practice for several years where he allows his loyal customers to purchase items on credit without the need for a written agreement. One day, John encounters financial difficulties and decides to implement a new policy wherein customers must sign a written agreement before being allowed to avail of credit. One of his long-standing customers, Maria, is surprised by this new requirement and refuses to sign the agreement. Maria argues that John cannot suddenly change the terms of their agreement without her consent.

Question: Discuss the effect and application of the principle of custom (Civil Code, Arts. 11-12) in the given scenario. Can John enforce the new policy requiring customers to sign a written agreement for credit transactions? Explain your answer with reference to applicable laws.