Honesty in Business: Making good on a deal

D'rabanan a transaction is only complete when the item being bought is taken under the protection of the buyer.
Until this time, the seller can reneg on the transaction.
If the price goes down, the buyer will want to reneg. If it goes up, the seller will want to reneg.
If one has the power to transfer the item, that person has an option.
Exercising this option is subject to a curse, even in halachah.
We have a few questions:
1. Why do the sages allow for the option but make it subject to a curse?
2. Why is the format of the curse what it is?
A curse is an appropriate punishment, because it aims to adjust the person's reputation appropriately.

מַאי טַעְמֵיהּ דְּרַב נַחְמָן? סָבַר לַהּ כְּרַבִּי יוֹחָנָן. דְּאָמַר: דְּבַר תּוֹרָה מָעוֹת קוֹנוֹת. וּמִפְּנֵי מָה אָמְרוּ מְשִׁיכָה קוֹנָה – גְּזֵירָה שֶׁמָּא יֹאמַר לוֹ: נִשְׂרְפוּ חִטֶּיךָ בָּעֲלִיָּיה.

Bava Metzia 46b:6

The Gemara inquires: What is the reason for the opinion of Rav Naḥman? The Gemara explains: Rav Naḥman holds in accordance with the opinion of Rabbi Yoḥanan, who says: By Torah law money effects acquisition, i.e., when one pays money he acquires the item, even if he has not yet performed another act of acquisition. And for what reason did the Sages say that pulling acquires an item and money does not? This is a rabbinic decree lest the seller say to the buyer after receiving the money: Your wheat was burned in the upper story. If a fire breaks out or some other mishap occurs after a seller receives the money, he will not bother to save the goods in his house because they no longer belong to him, and the buyer may incur a loss.

בבא מציעא מ״ד א:י״א

זֶה הַכְּלָל: כׇּל הַמִּטַּלְטְלִים קוֹנִין זֶה אֶת זֶה. כֵּיצַד? מָשַׁךְ הֵימֶנּוּ פֵּירוֹת וְלֹא נָתַן לוֹ מָעוֹת – אֵינוֹ יָכוֹל לַחְזוֹר בּוֹ. נָתַן לוֹ מָעוֹת וְלֹא מָשַׁךְ הֵימֶנּוּ פֵּירוֹת – יָכוֹל לַחְזוֹר בּוֹ.

Bava Metzia 44a:11

This is the principle: With regard to those who exchange all forms of movable property, each acquires the property of the other, i.e., the moment that one of the parties to the exchange takes possession of the item that he is acquiring, e.g., by means of pulling, the other party acquires the item from the first party. How so? If the buyer pulled produce from the seller, but the buyer did not yet give the seller their value in money, he cannot renege on the transaction, but if the buyer gave the seller money but did not yet pull produce from him, he can renege on the transaction, as the transaction is not yet complete.

בבא מציעא מ״ד א:י״ב

אֲבָל אָמְרוּ: מִי שֶׁפָּרַע מֵאַנְשֵׁי דּוֹר הַמַּבּוּל וּמִדּוֹר הַפְּלַגָּה – הוּא עָתִיד לְהִפָּרַע מִמִּי שֶׁאֵינוֹ עוֹמֵד בְּדִבּוּרוֹ.

Bava Metzia 44a:12

But with regard to the latter case, the Sages said: He Who exacted payment from the people of the generation of the flood, and from the generation of the dispersion, i.e., that of the Tower of Babel, will in the future exact payment from whoever does not stand by his statement. Just as the people of those generations were not punished by an earthly court but were subjected to divine punishment, so too, although no earthly court can compel the person who reneged to complete the transaction, punishment will be exacted at the hand of Heaven for any damage that he caused.

בבא מציעא מ״ח א:א׳

רַבִּי שִׁמְעוֹן אוֹמֵר: אַף עַל פִּי שֶׁאָמְרוּ טַלִּית קוֹנָה דִּינַר זָהָב וְאֵין דִּינַר זָהָב קוֹנֶה טַלִּית, מִכׇּל מָקוֹם כָּךְ הֲלָכָה. אֲבָל אָמְרוּ: מִי שֶׁפָּרַע מֵאַנְשֵׁי דּוֹר הַמַּבּוּל וּמֵאַנְשֵׁי דּוֹר הַפְּלַגָּה וּמֵאַנְשֵׁי סְדוֹם וַעֲמוֹרָה וּמִמִּצְרַיִם בַּיָּם – הוּא עָתִיד לִיפָּרַע מִמִּי שֶׁאֵינוֹ עוֹמֵד בְּדִיבּוּרוֹ.

Bava Metzia 48a:1

Rabbi Shimon says: Even though the Sages said that when one party takes possession of a garment, the other party acquires a gold dinar, but when one party takes possession of a gold dinar, the other party does not acquire a garment, in any case, that is what the halakha would be. But the Sages said with regard to one who reneges on a transaction where one party pulled the gold dinar into his possession: He Who exacted payment from the people of the generation of the flood, and from the people of the generation of the dispersion, and from the inhabitants of Sodom and Gomorrah, and from the Egyptians in the Red Sea, will in the future exact payment from whoever does not stand by his statement.

בבא מציעא מ״ח א:ב׳

וְהַנּוֹשֵׂא וְנוֹתֵן בִּדְבָרִים – לֹא קָנָה, וְהַחוֹזֵר בּוֹ – אֵין רוּחַ חֲכָמִים נוֹחָה הֵימֶנּוּ.

Bava Metzia 48a:2

The baraita concludes: And one who negotiates, where the negotiation culminates with a statement committing himself to acquire the item, did not acquire the item without a formal act of acquisition. But with regard to one who reneges on his commitment, the Sages are displeased with him.

בבא מציעא מ״ח א:ג׳

וְאָמַר רָבָא: אָנוּ אֵין לָנוּ אֶלָּא ״אֵין רוּחַ חֲכָמִים נוֹחָה הֵימֶנּוּ״. דְּבָרִים וְאִיכָּא בַּהֲדַיְיהוּ מָעוֹת – קָאֵי בַּ״אֲבָל״. דְּבָרִים וְלֵיכָּא בַּהֲדַיְיהוּ מָעוֹת – לָא קָאֵי בַּ״אֲבָל״.

Bava Metzia 48a:3

And Rava says: With regard to one who reneges on his commitment, we have only the statement that the Sages are displeased with him, but not that he is subject to a curse. The Gemara explains: If there is a statement of commitment and there is the payment of money accompanying it, he stands subject to the curse: But the Sages said: He Who exacted payment. If there is a statement of commitment and there is no payment of money accompanying it, he does not stand subject to the curse: But the Sages said: He Who exacted payment.

בבא מציעא מ״ט א:ו׳

מֵיתִיבִי, רַבִּי יוֹסֵי בְּרַבִּי יְהוּדָה אוֹמֵר: מָה תַּלְמוּד לוֹמַר ״הִין צֶדֶק״, וַהֲלֹא ״הִין״ בִּכְלַל אֵיפָה הָיָה? אֶלָּא לוֹמַר לָךְ: שֶׁיְּהֵא הֵן שֶׁלְּךָ צֶדֶק, וְלָאו שֶׁלְּךָ צֶדֶק. אָמַר אַבָּיֵי: הָהוּא שֶׁלֹּא יְדַבֵּר אֶחָד בַּפֶּה וְאֶחָד בַּלֵּב.

Bava Metzia 49a:6

The Gemara raises an objection: Rabbi Yosei, son of Rabbi Yehuda, says: What is the meaning when the verse states: “A just ephah, and a just hin, shall you have” (Leviticus 19:36)? But wasn’t a hin included in an ephah? Why is it necessary to state both? Rather, this is an allusion that serves to say to you that your yes [hen] should be just, and your no should be just. Apparently, it is a mitzva for one to fulfill his promises. Abaye says: That verse means that one should not say one matter with his mouth and think one other matter in his heart. It is prohibited for one to make a commitment that he has no intention of fulfilling. Rav Kahana made his commitment in good faith and reneged due to changed circumstances. That is not prohibited.

בבא מציעא מ״ט א:ה׳

דְּאִיתְּמַר: דְּבָרִים, רַב אָמַר: אֵין בָּהֶן מִשּׁוּם מְחוּסְּרֵי אֲמָנָה, וְרַבִּי יוֹחָנָן אָמַר: יֵשׁ בָּהֶם מִשּׁוּם מְחוּסְּרֵי אֲמָנָה.

Bava Metzia 49a:5

The Gemara comments: This is as it was stated: There is an amoraic dispute with regard to reneging on a verbal commitment that was unaccompanied by an act of acquisition. Rav says: It does not constitute an act of bad faith. And Rabbi Yoḥanan says: It constitutes an act of bad faith.

בבא מציעא מ״ט א:ט״ז

אָמַר רַב פַּפֵּי, אָמַר לִי רָבִינָא: לְדִידִי אֲמַר לִי הָהוּא מֵרַבָּנַן וְרַב טָבוּת שְׁמֵיהּ, וְאָמְרִי לַהּ רַב שְׁמוּאֵל בַּר זוּטְרָא שְׁמֵיהּ, דְּאִי הֲווֹ יָהֲבִי לֵיהּ כֹּל חֲלָלָא דְעָלְמָא לָא (הֲוֵי קָא) [הָוֵה] מְשַׁנֵּי בְּדִבּוּרֵיהּ...

Bava Metzia 49a:16

Rav Pappi said that Ravina said to me: One of the Sages, and Rav Tavot is his name, and some say Rav Shmuel bar Zutra is his name, and he is one who even if they were to give him the entire expanse of the world he would not deviate from the truth in his speech...

בבא מציעא מ״ח ב:ב׳

אֲבָל אָמְרוּ מִי שֶׁפָּרַע וְכוּ׳. אִיתְּמַר, אַבָּיֵי אָמַר: אוֹדוֹעֵי מוֹדְעִינַן לֵיהּ. רָבָא אָמַר: מֵילָט לָיְיטִינַן לֵיהּ.

Bava Metzia 48b:2

§ The mishna teaches with regard to one who reneges on a transaction after the money was paid: But the Sages said: He Who exacted payment from the people of the generation of the flood, and from the generation of the dispersion, will in the future exact payment from whoever does not stand by his statement. It was stated that there is an amoraic dispute. Abaye said that we inform one who seeks to renege on a transaction: Be aware that this is the punishment of one who does not stand by his statement. Rava said that we curse him with that statement.

בבא מציעא מ״ח ב:ג׳

אַבָּיֵי אָמַר: אוֹדוֹעֵי מוֹדְעִינַן לֵיהּ, דִּכְתִיב: ״וְנָשִׂיא בְעַמְּךָ לֹא תָאֹר״. רָבָא אָמַר: מֵילָט לָיְיטִינַן לֵיהּ, דִּכְתִיב: ״בְּעַמְּךָ״ – בְּעוֹשֶׂה מַעֲשֵׂה עַמְּךָ.

Bava Metzia 48b:3

The Gemara elaborates: Abaye said that we inform him, as it is written: “Nor curse a ruler among your people” (Exodus 22:27), from which it is derived that it is prohibited to curse a ruler or any other member of the Jewish people. Rava said that we curse him, and the prohibition against cursing is not a concern, as it is written: “Among your people,” from which it is derived that the prohibition applies only with regard to one who performs an action befitting your people, not one who reneges on a transaction after the money is paid.

שולחן ערוך, חושן משפט ר״ד:א׳

אימתי מקבל החוזר בו מי שפרע ומתי נקרא מחוסר אמנה ובו י"א סעיפים:
מי שנתן דמים ולא משך המטלטלים אף ע"פ שלא נקנו לו המטלטלים כמו שנתבאר כל החוזר בו בין לוקח בין מוכר לא עשה מעש' ישראל וחייב לקבל מי שפרע ואפי' לא נתן אלא מקצת הדמים:

Shulchan Arukh, Choshen Mishpat 204:1

Someone who gives money but didn't take the items - even though he didn't formally acquire the items, as we will explain, anyhone who renegs, whether the buyer or the seller, does not act like the "behavior of Israel" and is required to accept the curse "who takes etc." and this is even if he only gave part of the money.

שולחן ערוך, חושן משפט ר״ד:ד׳

כיצד מקבל מי שפרע אוררין אותו בב"ד ואומרים מי שפרע מאנשי דור המבול ומאנשי דור הפלגה ומאנשי סדום ועמורה וממצרים שטבעו בים הוא יפרע ממי שאינו עומד בדבורו (וי"א שאומרים לו הוא יפרע ממך אם אינך עומד בדיבורך (טור בשם הרא"ש) וי"א שאומרים לו ברבים) (מרדכי ס"פ הזהב) :

Shulchan Arukh, Choshen Mishpat 204:4

How does one accept the "one who takes etc"? They curse him in the court and say "Who extracted from the men of the generation of the flood, and from the men of the genration of the dispersion, and from the people of Sodom and Gommorrah, and from Egypt when they were drowned at the sea, he will extract from someone who doesn't stand by what he says"