Renting a home-Who is obligated to place the Mezuzah?
One who rents a home from his friend, the renter is the one who is obligated to place the Mezuzahs by the doors, and to mend the area for the Mezuzah to be placed.
One rented the home on condition that it contain Mezuzos: Even if one rented the home on assumption [Chazaka, or even on condition] that it has Mezuzahs on its doors, and later discovered that it does not have Mezuzos, nevertheless the contract remains valid.
 Michaber Y.D. 291:2; C.M. 314:2; Bava Metzia 101b
 This means that if the doorpost is made of stone and requires drilling then he must do so and not the landlord. [See Rashi ibid]
 Rama 291:2; Beis Yosef in name of Rabbeinu Menucha; See Admur 437:7
If one rented the home on condition it does not have Mezuzos and discovered that it has Mezuzos: See Birkeiy Yosef 291, brought in Shaareiy Teshuvah 391:5
 See Admur ibid for a dispute in this matter and that the landlord may say he follows the lenient opinion