Daniel Gray asks:

If one learns lemaskana that R Yehudah in Braisah (50b) argues with mishnah on 51a, or according to hava amennah that this is so, is R Yehudah's din that a seller has upper hand and thus may be chozer on the transaction a din min hatorh or midirbannon? Either way, what is the reason to afford only the seller this advantage? On 51a the gmara discusses a different advantage afforded to sellers of the sirsor category - they even less than one-sixth they can be chozer, which Rashi explains is due to their livelihood. This reason was not applied to the din of one-sixth, so the answer to this question would appear to need to be different than that.

Daniel Gray, TORONTO Canada

The Kollel replies:

The Shitah Mekubetzes (51a, DH v'Z'l ha'Ritzbash) writes that Rebbi Yehudah ha'Nasi gives the seller the upper hand because he follows the reasoning of "Zavin Avid," as stated in the Gemara on 51a; the seller loses out when he sells. According to this, it appears that it could be a d'Oraisa logic.

Kol Tuv,

Dovid Bloom