מי שפרע - דרשה לפרשת נח

How so? If the buyer pulled produce from the seller, but the buyer did not yet give the seller their value in money, he cannot renege on the transaction, but if the buyer gave the seller money but did not yet pull produce from him, he can renege on the transaction, as the transaction is not yet complete. But with regard to the latter case, the Sages said: He Who exacted payment from the people of the generation of the flood, and from the generation of the dispersion, i.e., that of the Tower of Babel, will in the future exact payment from whoever does not stand by his statement. Just as the people of those generations were not punished by an earthly court but were subjected to divine punishment, so too, although no earthly court can compel the person who reneged to complete the transaction, punishment will be exacted at the hand of Heaven for any damage that he caused. Rabbi Shimon says: Anyone who has the money in his possession has the advantage. The Sages said it is only with regard to the seller that payment of money does not effect a transaction, so that if the buyer paid for the item and did not yet take possession of the purchase item, the seller can renege on the sale and return the money. By contrast, once the buyer paid for the item he cannot renege on his decision and demand return of his money, even if he did not yet take possession of the purchase item.