Bava Metzia 50A

שוה שש בחמש, מי נתאנה ⁠– מוכר, יד מוכר על העליונה. רצה אומר לו: ״תן לי מקחי״, או ״תן לי מה שאוניתני״.

an item worth 6 ma’a for 5 ma’a, who was exploited? It is the seller. Therefore, the seller is at an advantage. If he wishes, he can say to the buyer: Give me back my merchandise and nullify the transaction, or he can say: Give me back the sum which you received by engaging in exploitation of me.

איבעיא להו: פחות משתות לרבנן, לאלתר הויא מחילה, או בכדי שיראה לתגר או לקרובו? ואם תמצי לומר בכדי שיראה לתגר או לקרובו, מאי איכא בין שתות לפחות משתות?

§ A dilemma was raised before the rabbis: According to the opinion of the Rabbis that one has only until a period of time has passed that would allow him to show the merchandise to a merchant or to his relative in order to claim that he has been exploited, in a case where the disparity between the value of the purchase item and the price paid is less than 1/6th, is there a waiver of the discrepancy and therefore the transaction is finalized immediately, or in this case as well, is the transaction finalized only after the time that it takes the buyer to show the merchandise to a merchant or to his relative? And in addition, if you say that the transaction is finalized only after the time that it takes to show the merchandise to a merchant or to his relative, what difference is there between a disparity of 1/6th and a disparity of less than 1/6th?

איכא דאלו שתות ⁠– ידו על העליונה, רצה ⁠– חוזר, רצה ⁠– קונה ומחזיר אונאה. ואילו פחות משתות ⁠– קנה, ומחזיר אונאה.

The Talmud answers: There is a difference, as in the case of a disparity of 1/6th, the one who was exploited has the advantage, since if he wishes, he reneges on the transaction, and if he wishes, the buyer acquires the purchase item, and the one who perpetrated the exploitation returns the sum gained through his exploiting the other, while in the case of a disparity of less than 1/6th, the buyer acquires the purchase item, and the one who perpetrated the exploitation returns the sum gained through his exploiting the other, but there is no option of nullifying the transaction.