Related for Ketubot 11:4
אַלְמָנָה שֶׁהָיְתָה כְתֻבָּתָהּ מָאתַיִם וּמָכְרָה שָׁוֶה מָנֶה בְמָאתַיִם אוֹ שָׁוֶה מָאתַיִם בְּמָנֶה, נִתְקַבְּלָה כְתֻבָּתָהּ. הָיְתָה כְתֻבָּתָהּ מָנֶה וּמָכְרָה שָׁוֶה מָנֶה וְדִינָר בְּמָנֶה, מִכְרָהּ בָּטֵל. אֲפִלּוּ הִיא אוֹמֶרֶת אַחֲזִיר אֶת הַדִּינָר לַיּוֹרְשִׁין, מִכְרָהּ בָּטֵל. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, לְעוֹלָם מִכְרָהּ קַיָּם עַד שֶׁתְּהֵא שָׁם כְּדֵי שֶׁתְּשַׁיֵּר בְּשָׂדֶה בַּת תִּשְׁעָה קַבִּים, וּבְגִנָּה בַּת חֲצִי קַב, וּכְדִבְרֵי רַבִּי עֲקִיבָא בֵּית רֹבַע. הָיְתָה כְתֻבָּתָהּ אַרְבַּע מֵאוֹת זוּז, וּמָכְרָה לָזֶה בְמָנֶה וְלָזֶה בְמָנֶה וְלָאַחֲרוֹן יָפֶה מָנֶה וְדִינָר בְּמָנֶה, שֶׁל אַחֲרוֹן בָּטֵל וְשֶׁל כֻּלָּן מִכְרָן קַיָּם:
If the kethubah of a widow were for two manah, and she sold (property from the inheritance) worth one manah for two manah; or the value of two manah for one manah, she has received her inheritance. [For we say to her: "It is your loss." And with the value of one manah for two manah, even though she has gained, she cannot say: "It is my gain," for if one sends his messenger to the marketplace to trade, and he purchases something cheap, everything belongs to him who gave the money. We learn from here only about something which has no fixed price, such as land, which is wont to be sold by estimate; sometimes more, sometimes less. But if something has a fixed price and the messenger bought it for less, the ruling is not clear from (what we learn) here. I have found the rabbis to differ on this, and it would seem to me that (in such an instance) the messenger and the sender divide.] If her kethubah were a manah, and she sold the value of a manah and a dinar for a manah, her sale is void. [For she was not permitted to sell that dinar, so that the entire sale is "in error," the whole sale having taken place at one time.] Even if she says: I shall return a dinar to the heirs, her sale is void. R. Shimon b. Gamliel says: Her sale is always valid [and she returns the dinar to the heirs. For what did she make them lose?] — unless there is [such a great overcharge] that there would remain [in the absence of that overcharge] in a field, nine kavs [the size of a field], and in a garden, a half kav [the size of a garden.] And, according to R. Akiva, a quarter of a kav. [The halachah is not in accordance with R. Shimon b. Gamliel.] If her kethubah were four hundred zuz, and she sold to each one (of three buyers the value of a manah) for a manah; and to the last, the value of a manah and a dinar for a manah — the last (sale) is void, and all the others, valid.