Halakhah sobre Baba Metziá 6:9

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).

Halachah grants much flexibility regarding monetary law if both parties consent. Moreover, if a community has adopted a particular practice regarding a monetary matter, common custom, generally speaking, overrides Halachah (minhag mevateil halachah; see Yerushalmi Bava Metzia 7:1). A classic example is presented in the Mishnah (Bava Metzia 6:1), which states that an employer cannot insist that his employees work from dawn to dusk if the local custom among hired workers is not to work such hours.