What responsibility does a seller have to guarantee his product after the buyer has taken possession of it?
According to the Mishna (97b) if someone sells wine to his friend and it becomes vinegar, he is not responsible for it. The rishonim point out that we are dealing with a case where we are certain that the product was wine at the time of the sale, which puts the onus of responsibility on the buyer, since the wine “went bad” after he already owned it, allowing the seller to argue that it was the buyer’s casks that caused the problem.
Our Gemara quotes Rabbi Yosei b’Rabbi Ḥanina who rules that the case of the Mishna is only when the wine has been moved into the casks of the purchaser. If, however, it remained in the casks of the seller, then the buyer can demand that the seller take back his casks together with the wine, or, more correctly, the vinegar, and return his money. The Ra’avad explains Rabbi Yosei’s position as based on his belief that good wine will not turn to vinegar under ordinary circumstances, so if this wine did become vinegar it is an indication that there was something wrong with it from the very beginning, which allows the buyer to insist on a refund.
The Gemara points out that Rabbi Hiyya bar Yosef disagrees with this ruling. Based on a passage in Habakkuk (2:5) that describes the “treachery” of wine that rebels against a haughty person, he believes that wine spoiling is essentially a rebuke to the owner of the wine – it is his “bad luck” and therefore, his loss. The Rashbam explains that this is a type of midah ke-neged midah – the person gets what he deserves – in the sense that someone who tries to show off qualities that he does not have is punished by his wine – that appears to have the qualities of fine wine, but really is vinegar.