(based on Halacha Psuka vol.29, condensation of a psak from Darchei Hora’ah VI, pp. 151-162)

Case:

Ruling: The Ri Migash (Shut 51) says that if an object is sold with a blemish that, after fixing, would be considered like a different object, the sale can be voided¬ against the will of the seller even if he wants to fix it. On one hand, in our case, fixing entails bolstering the existing courtyard wall, which is a major change. However, since it is possible to do things unrelated to the home in order to remove danger, it may not be considered that there is an intrinsic flaw in the home itself.
However, a claim of mekach ta’ut is applicable for a different reason. The gemara (Pesachim 4b) says that the reason that the rental of a house before Pesach that did not have bedikat chametz done is not void is that a person does not mind doing an unexpected bedikat chametz. Some ask that there should be no question of voiding in the first place, just reducing the rental price, because the house itself is not blemished. The Netivot Hamishpat (233:4) answers that a house that is not fit for use, even due to an external factor, is considered as if it has a blemish within it. This is the situation in our case where the house is not livable considering the danger. Based on the Perisha (CM 232:5), who distinguishes between a simple and a complex/expensive fixing job, there are again grounds to void the sale. Yet beit din decided that the sale should not be voided based on the Divrei Malkiel (II, 85), who says that when the buyer does not express interest to void the sale, the seller cannot unilaterally void it.
The Rosh (Shut 96:6) says that when someone sells a house with broken windows or doors there is no bitul mekach, but the seller must take off the cost of repairs from the sales price. It sounds that the seller pays for the fixing but the buyer is the one who has to carry it out. This makes sense if the idea that a damager is responsible to toil to limit the loss is an exception, learned from a special pasuk (see Choshen Mishpat 403:3). It is possible, though, that damages are different, as the idea would have been, if not for the pasuk, to pay, not to restore. In contrast, regarding a sale, the idea is to present the buyer with a useful object, requiring the toil as well to make that possible. This was indeed beit din’s conclusion.
Beit din required def to pay for a professional, supervised team to make repairs to the level required by legally recognized basic standards in order to remove danger