Reference for Bava Metzia 100:9
תניא כותיה דרבא אונאה פחות משתות נקנה מקח יתר על שתות בטל מקח שתות קנה ומחזיר אונאה דברי רבי נתן רבי יהודה הנשיא אומר יד מוכר על העליונה רוצה אומר לו תן לי מקחי או תן לי מה שאניתני וזה וזה בכדי שיראה לתגר או לקרובו:
But if you say that in the case of annulment of sale, on the view of the Rabbis, one can always retract, why did they revert [etc.]? Surely R. Tarfon's ruling was more advantageous to them, since he declared overreaching [returnable] the whole day, but no more! — Annulment of sale is rare.<span class="x" onmousemove="('comment',' Therefore they did not regard the shorter period of R. Tarfon as particularly advantageous to them, the more so since a whole day is ample time for the defrauded party to discover that he was overreached. On the other hand, in respect of overreaching as distinct from annulment the longer period given by R. Tarfon (a whole day, as against the Rabbis', 'within the time necessary to shew the purchase to a merchant') was definitely to their disadvantage, and therefore they reverted to the ruling of the Rabbis. ');"><sup>9</sup></span>