פירוש על בבא בתרא 5:6

ד' מידות – laws divided one from the other.

There are four rules with regards to those who sell:
If one has sold good wheat and it turns out to be bad, the buyer can retract.
If he sold bad wheat and it is found to be good, the seller can retract.
[But if one sold] bad wheat and it is found to be bad, or good wheat and it is found to be good, neither may retract.
[If one has sold] dark wheat and it turned out to be white; Or white and it turned out to be dark; Or [if he sold] olive wood and it turned out to be sycamore wood; Or sycamore wood and it turned out to be olive wood; Or [if he sold] wine and it turned out to be vinegar; Or vinegar and it turned out to be wine; Either of them may retract.
Mishnah six begins to discuss certain ethical principles in the laws of selling and buying and their consequences on the validity of the sale. This is a topic which will be discussed through the middle of chapter six.
As stated at the beginning of the mishnah, there are four rules with regards to retracting a sale. These rules are contained in sections 1-4. (1) If a person sold something that was supposed to be good and it turned out to be bad, the buyer can retract. (2) If a person sold something that was supposed to be bad and it turned out to be good, the seller can retract. (3) If a person sold something and it turned out to be what he sold, the sale is final and no one may retract. (4) Finally, if a person sold something and it turned out to be different from what he sold, not necessarily better or necessarily worse, either of them may retract.

מכר לו חטים יפות – he made a stipulation with him that he should give him nice wheat and they were found to be bad. It is like overreaching/אונאה ; therefore, he (i.e., the buyer) can retract – whomever feels imposed upon/one’s self overreached alone, which is the purchaser, but the seller is not able to retract, and even if the wheat increased greatly in value.

אין אחד מהן יכול לחזור בו – even if they increased in value or became cheaper, for the purchaser is not able to say: “I intended for the beautiful ones, and this one who might say they are bad, because the purchaser tells him: “what is bad is bad.” And similarly, the opposite, that the seller is not able to state that I intended for the bad ones. And this one that I might say are good, it is the manner of the seller to state the bad ones become good ones.

שחמתית – reddish (Genesis 30:35): “and all the dark-colored [sheep], which we translate in Aramaic as שחום/dark, black (or brown).

ונמצאת לבנה – there are those for whom it is pleasant with this, and there are those for whom it is pleasant with that. But in this manner, it is an errant transaction for both of them, and both of them can retract, for if it was supposed to “nice ones,” and it turned out to be “bad ones,’ everyone enjoys “good ones.”

יין ונמצא חומץ – there are those who are pleased with wine, and there are those who are pleased with vinegar.