Kiddushin 42b:3קידושין מ״ב ב:ג׳
Rava says: That which we said, that with regard to less than one-sixth the transaction is valid and the item is acquired, we said only in a case where the brother receiving a smaller share did not appoint an agent to deal with the distribution on his behalf. But if the brother receiving a smaller share appointed an agent, this halakha does not apply, as the one who appointed the agent can say: I sent you to act for my benefit and not to my detriment. The agent’s right to act in this capacity did not extend to a case where it was to the detriment of the one who appointed him.
אָמַר רָבָא: הָא דַּאֲמַרַן ״פָּחוֹת מִשְּׁתוּת – נִקְנֶה מִקָּח״ – לָא אֲמַרַן אֶלָּא דְּלָא שַׁוְּיֵהּ שָׁלִיחַ, אֲבָל שַׁוְּיֵהּ שָׁלִיחַ, אָמַר: לְתַקּוֹנֵי שַׁדַּרְתָּיךָ וְלָא לְעַוּוֹתֵי.
Ketubot 85a:7כתובות פ״ה א:ז׳
The Gemara comments: And this is not so; Rav Ashi’s ruling is not accepted as halakha. Whether the instructions were given in this manner or whether the instructions were given in that manner, the agent must pay, as the one who appointed him can say to him: I sent you to act for my benefit, and not to my detriment. His right to act as an agent did not extend to a case where it was to the detriment of the one who designated him.
וְלָא הִיא, בֵּין כָּךְ וּבֵין כָּךְ מְשַׁלֵּם. דְּאָמַר לֵיהּ: ״לְתַקּוֹנֵי שַׁדַּרְתָּיךָ וְלָא לְעַוּוֹתֵי״.
Bava Metzia 108a:14בבא מציעא ק״ח א:י״ד
In the converse case, if he bought it for two hundred dinars and the field was worth one hundred dinars, the Sages understood that the neighbor can say to the buyer: I sent you to act for my benefit, but not to act to my detriment. Since the field will not remain in your possession, you are effectively my agent, and I am not prepared to pay more than its market value due to your mistake. Mar the Elder, son of Rav Ḥisda, said to Rav Ashi: This is what the Sages of Neharde’a say in the name of Rav Naḥman: There is no exploitation with regard to real estate, as land has no fixed value, and therefore it cannot be said that the buyer overpaid, and he is given whatever sum he spent.
זְבַן בְּמָאתַן וְשָׁוְיָא מְאָה, סְבוּר מִינָּה, מָצֵי אָמַר לֵיהּ: לְתַקּוֹנֵי שַׁדַּרְתָּיךָ וְלָא לְעַוּוֹתֵי. אֲמַר לֵיהּ מָר קַשִּׁישָׁא בְּרֵיהּ דְּרַב חִסְדָּא לְרַב אָשֵׁי: הָכִי אָמְרִי נְהַרְדָּעֵי מִשּׁוּם דְּרַב נַחְמָן: אֵין אוֹנָאָה לְקַרְקָעוֹת.
Bava Batra 169b:11בבא בתרא קס״ט ב:י״א
Rav Naḥman said to the agent: The principle with regard to an agent is that if he acts to the detriment of the one who appointed him, the one who appointed him can say: I sent you to act for my benefit and not to my detriment. Therefore, the entire agency is null and void, thereby negating the purchase. Nevertheless, you agreed to purchase the land without a guarantee. Therefore, go yourself and purchase the land from him without a guarantee, and then sell it to this woman with a guarantee that you will reimburse her in the event the land is repossessed.
אֲמַר לֵיהּ: ״לְתַקּוֹנֵי שַׁדַּרְתָּיךָ, וְלָא לְעַוּוֹתֵי. זִיל זִבְנַהּ מִינֵּיהּ שֶׁלֹּא בְּאַחְרָיוּת, וַהֲדַר זַבְּנַהּ נִיהֲלַהּ בְּאַחְרָיוּת״.
Ketubot 99b:10כתובות צ״ט ב:י׳
He replied to them: This applies only where the homeowner erred, e.g., where he sold land for less than its market value. In that case, he cannot claim that the sale is invalid because of fraud. However, in a case where the agent erred, the homeowner can say to the agent: I sent you to act for my benefit and not to my detriment, and his appointment as an agent is nullified.
הָנֵי מִילֵּי הֵיכָא דִּטְעָה בַּעַל הַבַּיִת, אֲבָל טְעָה שָׁלִיחַ, אֲמַר לֵיהּ: ״לְתַקּוֹנֵי שַׁדַּרְתָּיךָ וְלָא לְעַוּוֹתֵי״.
Bekhorot 61a:10בכורות ס״א א:י׳
It was stated: In the case of one who says to his agent: Go and separate animal tithe on my behalf, Rav Pappi says in the name of Rava: If he called the ninth animal the tenth, it is sanctified and may not be eaten until it has developed a blemish. The owner is not particular about this error, as the animal is not rendered entirely prohibited. But if he designated the eleventh animal as the tenth it is not sanctified as a peace offering, as the owner would not tolerate losing the animal entirely. And Rav Pappa disagrees and says: Even if the agent called the ninth animal the tenth it is not sanctified, as the owner who sent him can say to him: I sent you to act for my benefit and not to my detriment. The authority to serve as an agent does not extend to a case where he acts to the detriment of the one who designated him.
אִיתְּמַר: הָאוֹמֵר לִשְׁלוּחוֹ ״צֵא וְעַשֵּׂר עָלַי״, רַב פַּפִּי מִשְּׁמֵיהּ דְּרָבָא אָמַר: קָרָא לַתְּשִׁיעִי ״עֲשִׂירִי״ — קָדוֹשׁ, וְלָאַחַד עָשָׂר ״עֲשִׂירִי״ — אֵינוֹ קָדוֹשׁ. וְרַב פָּפָּא אָמַר: אֲפִילּוּ קָרָא לַתְּשִׁיעִי ״עֲשִׂירִי״ — אֵינוֹ קָדוֹשׁ, דְּאָמַר לֵיהּ: לְתַקּוֹנֵי שַׁדַּרְתָּיךָ וְלָא לְעַוּוֹתֵי.