“But our warranty policy specifies replacing the defective part,” argued Mr. Cahane.
“The overriding principle in commerce is hakol keminhag hamedina, everything is accordance with the local commercial practice,” replied Rabbi Dayan. “While halacha provides default rules in the absence of a common practice, people conduct business with the understanding of the common practice. (See Maharsham 3:28)
“Thus, in a regular commercial setting, such as when buying a computer from a store that operates with normal warranty policy, the policy is binding,” concluded Rabbi Dayan. “In an informal setting, such as if one had bought the computer second-hand from his friend, we would apply the halachic rulings, since here the common commercial practice is not applicable.”