Mekach Taus – Defects and wrong charge:[1]

Even in the event that a fully valid acquisition has taken place between the buyer and seller, or giver and recipient, to legalize the transaction, nonetheless, in the event of a Halachically defined Mekach Taus, it is permitted for the party who was wronged[2] to retract from the sale [as in truth the sale is viewed as if it never took place[3]]. It is beyond the scope of this article to delineate the various legal definitions of Mekach Taus which permit retracting from a sale and receiving whatever money he gave back in return, although some of the main examples include 1) A blemished product, or product not fitting description at time of purchase.[4] 2) Overcharging or under charging for the product more than 20%, which is known as Onah.[5] There are various details in these two categories and hence a Rav is to be contacted in all cases that the buyer and seller cannot reach an agreement for a requested refund.

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[1] See Michaber C.M. Chapters 227-234 regarding general law of Mekach Taus and Onah; Encyclopedia Talmudit Erech Onah

[2] May the perpetrator [i.e. Mianeh] retract from the sale? The party who did the wrong may not retract from the sale if the victim [i.e. Misaneh] consents to go through with the sale regardless, either verbally or through silence. However, if the victim does not give his consent to go through with the sale in the above manner, then it is disputed as to whether the perpetrator may on his own decide to nullify the sale. [Michaber 227:4 rules he may not, as Lo Yihyeh Choteh Niskar; Rama ibid rules he may because the sale is invalid; See Smeh 227:6-8]

[3] See Smeh 227:8

[4] See Michaber C.M. 228-234

[5] See Michaber C.M. 227:4; See also Admur C.M. Hilchos Onah