But if the loss to the purchaser cannot be reimbursed from the purchasing money by returning it, e.g., if the seller spent it already, let the purchaser take the ox itself in lieu of the money, as people say: Allow yourself to be repaid by your debtors even in bran, since anything may be used as payment for a debt. In the event that the seller has no money with which to reimburse the purchaser, even if it is a mistaken transaction the result may be that the purchaser keeps the ox in lieu of having his money returned. Accordingly, there would be no practical difference between the opinions of Rav and Shmuel.
לא צריכא, דאיכא לאשתלומי מיניה.
The Talmud answers: No, it is necessary for them to engage in a dispute in a case where the seller does have sufficient funds from which to repay the purchaser, and the purchaser demands that his money be returned as opposed to keeping the ox as payment.
רב אמר הרי זה מקח טעות – זיל בתר רובא, ורובא דאינשי לרדיא הוא דזבני. ושמואל אמר, יכול שיאמר לו ״לשחיטה מכרתיו לך״ – ולא אזלינן בתר רובא. כי אזלינן בתר רובא – באיסורא, אבל בממונא – לא אזלינן בתר רובא, אלא המוציא מחבירו עליו הראיה.
The Talmud now explains the logic of Rav and Shmuel: Rav says that this is a case of a mistaken transaction, due to the principle: Follow the majority, and the majority of people buy oxen for plowing. And Shmuel says that the seller can say to him: I sold it to you for slaughtering, and we do not follow the majority in this case. When do we follow the majority according to Shmuel? Only in determining the prohibited or permitted status of an item. But in monetary matters such as this, we do not follow the majority. Rather, the operative principle is that the burden of proof rests upon the claimant.