Al pi Halacha is one obligated to pay for the loss of time that a rental car is in the body shop? The rental companies usually charge you the full rental for those days that they ar unable to rent it because of damage that the renter was responsible for. If it is not in the contract is there any halachic support for or against this practice. If possible please include mareh mekomos. (Does the sugya on the bottom of 20a Baba Kama have any bearing?)
This is a case of mevatel kiso shel chavero–the rental company was prevented from making income. Under circumstances where a definite loss of income is caused, some authorities write that the person causing the damage is obligated to pay (see Panim Me’iros 1:82; Zayis Raanan 2:16; Giddulei Shmuel (Bava Metzia 76); Pilpula Charifta; among others). This opinion is also found among rishonim (Rama, brought in Nimmukei Yosef, Bava Kama 20).
However, other rishonim and acharonim do not concur with this opinion. As you note, the sugya of Bava Kama 20 is pertinent, in that the person using another’s property, and causing a loss of rental, is only liable to pay when he actually lives in the house. If he were only to ‘steal’ the house but not to live in it, he would be exempt from payment even if a loss is caused. This ruling is given by Rema (363:6), and it implies that the person causing damage is exempt.
As the Vilna Gaon writes, the reason for this is that the loss is considered a grama, and the money cannot be extracted from the person who caused the damage.