Q: I rented a car from a Jewish-owned company. The rental contract specifies terms of liability that do not conform to the rules of shomrim. Are these terms halachically binding?

A: The rules of shomer chinam, shomer sachar, socher, and sho’el are default rules. However, the owner and guardian can stipulate whatever terms of liability they wish, whether more stringent or more lenient than those prescribed by the Torah. This is based on the rule of “kol tenai she’b’mamon kayam” (any stipulation in monetary matters is binding). Thus, the terms explicit in the contract are halachically binding (C.M. 296:5).

When the liability terms are stipulated from the beginning, there is no need for a kinyan. However, once the rental begins, an agreed change in the liability terms requires a kinyan, unless the owner explicitly exempted the guardian from his responsibility, which is a form of mechilah (forgoing) (Rama 344:1; Pischei Choshen, Pikadon 2:16; 10:7).

Additionally, for items that are completely excluded from liability of shomrim (e.g. real estate and documents, or cases of be’alav imo - when the owner is in the service of the guardian) a stipulation to obligate the guardian requires a kinyan (301:4; P.C., 2:17).