The Mishnah before us deals with a widow who sells land from the estate in order to collect her kesubah, and an error occurred in the sale. The question under discussion is: in which circumstances does the sale remain valid, and in which is it void?
She sold land worth a maneh for two hundred, or land worth two hundred for a maneh:
The Mishnah opens with a widow whose kesubah is two hundred zuz, and presents two opposite cases:
She sold a field worth a maneh (one hundred zuz) for two hundred - she has collected her kesubah in full, even though the land she sold was worth only one hundred. She made a profitable transaction here, and she cannot return to the estate and demand another hundred on the claim that she was entitled to collect two hundred from the property. Two hundred were due to her, and two hundred is what she received.
She sold a field worth two hundred for a maneh - here too her kesubah is considered collected in full, and even though in practice only one hundred zuz came into her hands, the kesubah is regarded as paid.
In both directions, then, her kesubah has been collected. It is worth noting that in the second case, where land worth two hundred was sold for a maneh, the orphans can raise a claim of overreaching and say that they do not want the sale to stand; but as long as they have not made such a claim, halachically the matter does not concern them, and the kesubah is considered paid even though she received only one hundred.
She sold more than the amount of her kesubah:
The Mishnah continues with a further case: her kesubah was a maneh, and she sold a field worth a maneh and a dinar - that is, one dinar more than the amount of her kesubah - for a maneh. Here the sale is null and void, for two reasons that combine with one another:
Because of the overreaching - she sold something worth a maneh and a dinar for a maneh alone.
Because she exceeded her authority - she was not given permission to sell more than the amount of her kesubah, and once she did something that was not permitted to her, her power to sell lapsed.
The Mishnah adds: "Afilu hi omeres achzir es hadinar layorshim" - even if she is willing to return that extra dinar, which was sold improperly, to the estate, her sale is void. The heirs have no interest in upholding the sale, and they have the right to annul it.
The view of Rabban Shimon ben Gamliel:
Rabban Shimon ben Gamliel disagrees and says: "Le'olam michrah kayam" - her sale always stands. In his view, even if she sold more than the amount of her kesubah, as long as she is willing to return the excess to the heirs, the sale stands. When does this apply? Only where the excess in the sale is of such a size that, were it not for it, the heirs would have been left with an area of land large enough to be called a field. If a field's measure remained in their hands, the sale is void; and if not, the matter does not invalidate it.
And these are the measures that were established:
For a field: an area for nine kabin - a space in which nine kabin of seed can be sown, which is three thousand seven hundred and fifty square amos.
For a garden (a place where vegetables are sown): an area for half a kav, which is two hundred eight and a third square amos.
For a garden, according to Rabbi Akiva: an area for a quarter kav - half of the previous measure, which is one hundred four and one sixth square amos.
She sold to several buyers:
The final case in the Mishnah: "Haysah kesubasah arba me'os zuz" - her kesubah was four hundred zuz, and she sold to one buyer for a maneh and to another for a maneh - three sales that were carried out properly - and to the last buyer she sold a field worth a maneh and a dinar for a maneh. In the previous case the discussion concerned a single sale in which an extra dinar was sold, whereas here the first three sales were valid, and only the fourth was carried out improperly.
Therefore the Mishnah says: "Shel acharon batel" - only the last sale is annulled, because in it she sold more than the amount of her kesubah. The remaining sales stand, since these were separate sales that were carried out properly.
In summary: we have learned that a widow who sold estate property for a price that does not match its value - whether she gained or lost - has collected her kesubah in both directions. But if she sold more than the amount of her kesubah, the sale is void according to the first Tanna, and even returning the excess to the heirs does not help. Rabban Shimon ben Gamliel upholds the sale, unless the heirs were left with the measure of a field or a garden according to the measures listed. And when she sold to several buyers one after another, only the last sale is annulled.