1) A "SHOMER SACHAR" WHO IS "MUDAR HANA'AH"
QUESTION: The Gemara discusses the Halachic status of the finder of a lost object. Does he have the status of a Shomer Chinam, a guardian who watches an object for free (whose liability is limited to negligence, Peshi'ah), or does he have the status of a paid guardian (whose liability extends to Geneivah and Aveidah)? Rabah maintains that the finder of a lost object is considered a Shomer Chinam. Rav Yosef maintains that he is considered a Shomer Sachar.
According to Rav Yosef, what pay does the finder receive such that he is considered a Shomer Sachar? Rav Yosef explains that since the finder is involved in a Mitzvah when he takes care of the lost object, he is exempt from giving Tzedakah to a poor person because of the principle of "ha'Osek b'Mitzvah Patur Min ha'Mitzvah" -- "One who is involved in one Mitzvah is exempt from another Mitzvah." The money he saves, called "Perutah d'Rav Yosef," is considered his payment for watching the lost object.
TOSFOS (DH v'Havei) quotes RABEINU CHANANEL and the BEHAG who prove from the Gemara in Nedarim (33b) that the Halachah follows the view of Rav Yosef. The Gemara there discusses whether a person who is forbidden by a Neder from benefiting from his friend ("Mudar Hana'ah") is allowed to return a lost object to him. According to one opinion there, such a person may not return a lost object to the owner because he would receive the benefit of "Perutah d'Rav Yosef," saving money while watching the object. The other opinion says that "Perutah d'Rav Yosef" is not common, and thus he may return the lost object. The Gemara implies that both opinions maintain that the finder is considered a Shomer Sachar; they disagree only about whether "Perutah d'Rav Yosef" is a common enough occurrence to prohibit a "Mudar Hana'ah" from returning a lost object.
Tosfos refutes this proof and says that even Rabah agrees that a person who is taking care of a lost object is exempt from giving Tzedakah, and thus both opinions in Nedarim may follow Rabah as well. Rabah's point of dispute with Rav Yosef is that Rabah maintains that the money the finder saves does not constitute payment for watching the lost object, and thus he is not a Shomer Sachar.
The MAHARSHAL (in YAM SHEL SHLOMO, Bava Kama 6:9) asks that the proof is difficult for a more basic reason. How is it even possible that the second opinion in Nedarim follows the view of Rav Yosef? If the finder has the status of a Shomer Sachar, he should not be permitted to pick up the object since he is "paid" to do so by its owner, from whom he may not derive benefit? If "Perutah d'Rav Yosef" is so uncommon, why should he be called a Shomer Sachar at all?
ANSWER: The EVEN HA'AZEL (Hilchos Aveidah 13:10) explains that the finder is considered a Shomer Sachar as long as he stands to gain from guarding the object. However, when a person is a "Mudar Hana'ah" and may not benefit from someone else, he is forbidden from having actual benefit, but not potential benefit. Since it is unlikely that the finder will encounter a poor person while he is taking care of the lost object, he is permitted to take a chance and pick up the object in order to return it, and he may assume that he will not encounter a poor person. (Y. Montrose)

29b----------------------------------------29b

2) DOES "EIN HA'SOCHER RASHAI L'HASKIR" APPLY TO LAND AND HOUSES?
OPINIONS: The Gemara quotes Rebbi who states that a renter may not rent to a third party the object he rented, and a borrower may not lend to someone else the object he borrowed. RASHI (DH Kan Shanah Rebbi) explains that the reasoning behind this Halachah is that the owner may say, "I only trusted you with my object, not anyone else."
Does this Halachah apply to all forms of property, including land and houses, or only to Metaltelin (movable objects) such as those discussed in the Gemara here?
(a) The RAMBAM (Hilchos Sechirus 5:2) writes that if one who rents a house wants to rent it out to someone else, he is permitted to do so as long as the number of people living in the house with the current renter is equal to or less than the number of people to whom he wants to rent it. The Rambam explains that the Chachamim's rule that a renter may not rent to a third party applies only to Metaltelin. Only in the case of Metaltelin can the owner claim that he did not want his object given to anyone else. However, in the case of land the owner cannot make such a claim. The Rambam apparently maintains that the owner may make such a claim only for Metaltelin because a movable object is prone to become damaged or lost, while houses and land are unlikely to be damaged or lost. The HAGAHOS MAIMONIYOS quotes the MAHARAM who cites proofs for the Rambam's ruling. The SHULCHAN ARUCH (CM 316:1) rules in accordance with the Rambam.
(b) The Rambam quotes a dissenting opinion that states that one may not rent an apartment to another renter. This seems to be the position of the RA'AVAD who mentions such an opinion and explains that since some people destroy a house when they live in it and fail to take care of it properly, the owner may claim that he did not want anyone else to use the house other than the person to whom he rented it.
The SHIMRU MISHPAT (ch. 70) writes that although the Halachah follows the Rambam, a renter should not rent out the house without the consent of the owner, or without an explicit condition in the contract permitting him to do so. Customs in monetary law have the status of Halachah, and thus one may not rent out the house without first consulting with the owner. This is also the opinion of the PISCHEI CHOSHEN (Hilchos Sechirus 4:22) and the MISHPETEI HA'TORAH (Sechirus). The Shimru Mishpat adds that if the renter rented out the house without permission from the owner, the owner has the right to collect any extra money which resulted from that rental (such as when the renter charged more than he was paying himself). (Y. Montrose)