1. how does mekach ta’ut work in modern purchases? the shulchan aruch in choshen mishpat 228:6 paskens that if an item has a defect the seller must inform the buyer. but when does an undisclosed defect actually cancel the whole sale? does the defect have to make the item unusable, or is it enough that most buyers would have paid less had they known?

2. the modern cases: a used car with a previous accident, a house with water damage inside the walls, a refurbished device sold without saying refurbished, an online product that looks materially different from the photos. which of these is a mum b’mekach that undoes the deal, and which is just disappointment?

3. the disclaimer side: if the contract says as is or all sales final, does that remove the buyer’s claim? can there be mechila on a defect the buyer did not know about? and how does minhag hamedinah, normal commercial practice, set what a buyer is entitled to expect?

4. and the seller’s side: does disclosing the defect always fix everything, or are there sales that disclosure cannot save?

bottom line: when can a buyer actually undo a purchase halachically, and when is the sale final?