Halakhah sobre Baba Metziá 7:14

Accordingly, “batter” should be excused from payment since the bat was broken as a result of normal usage. Moreover, the stipulation for payment should be invalid since it contradicts Torah law. Indeed, the Mishnah (Bava Metzia 7:11) states “kol hamatneh al mah shekatuv baTorah tena’o batel”, a stipulation that runs counter to Halachah is invalid.

However, the previous Mishnah (Bava Metzia 7:10) contradicts this rule. This Mishnah teaches that a borrower may make a condition that he excused from payment in all situations. The reasoning for this Mishnah is that tenai shebemammon kayam, that stipulations in regard to financial matters are valid even if they contradict Torah law. One owns his money so he may waive his Torah given right to collect money or conversely is permitted to agree to obligate himself to pay money that the Torah does not require him to pay.

We should note that Rav Goren concludes that the buyers have a right to be angry at the seller, since he did not act with the highest levels of integrity and morality (see Mishnah Bava Metzia 6:1). Practically speaking, such conduct by a seller is ill-advised, as he will not succeed in building a good reputation if he does not deliver the promised product in the fullest sense (see Mishnah Bava Metzia 7:5, which dictates to beit din to advise someone that even though the Halachah sides with him in his dispute, he damages his marketability due to his less-than-stellar conduct).