Halacha

הלכה א
הַמּוֹכֵר זֵרְעוֹנֵי גִּנָּה שֶׁאֵין עַצְמָן שֶׁל זֵרְעוֹנִים נֶאֱכָל לַחֲבֵרוֹ וְלֹא צָמְחוּ חַיָּב בְּאַחֲרָיוּתָן וּמַחֲזִיר לוֹ אֶת הַדָּמִים שֶׁלָּקַח מִמֶּנּוּ שֶׁחֶזְקָתָן לִזְרִיעָה. וְהוּא שֶׁלֹּא צָמְחוּ מֵחֲמַת עַצְמָן אֲבָל אִם לָקְתָה הָאָרֶץ בְּבָרָד וְכַיּוֹצֵא בּוֹ אֵינוֹ חַיָּב בְּאַחֲרָיוּתָן שֶׁמָּא מֵחֲמַת הַבָּרָד לֹא צָמְחוּ. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
1.
The following laws apply when a person sells seeds of garden vegetables to a colleague, when the seeds themselves are not eaten. If the seeds do not grow, the seller is responsible to reimburse him for the money that he took from him. For we can assume that he purchased the seeds to sow them.
The above applies provided that the seeds did not grow because of a problem with the seeds themselves. If, however, the reason they did not grow is that the land was smitten with hail or the like, the seller is not responsible for the loss, for perhaps the reason that the seeds did not grow is the hail. Similar principles apply in all analogous situations.

הלכה ב
מָכַר לוֹ זְרָעִים הַנֶּאֱכָלִין כְּגוֹן חִטִּים וּשְׂעוֹרִים וּזְרָעָן וְלֹא צָמְחוּ אֵינוֹ חַיָּב בְּאַחֲרָיוּתָן. אֲפִלּוּ הָיָה זֶרַע פִּשְׁתָּן שֶׁרֹב בְּנֵי אָדָם קוֹנִין אוֹתָהּ לִזְרִיעָה. הוֹאִיל וְאוֹכְלִין אוֹתָהּ אֵינוֹ חַיָּב בְּאַחֲרָיוּת זְרִיעָתוֹ. וְאִם הוֹדִיעוֹ שֶׁהוּא קוֹנֶה לְזֶרַע חַיָּב בְּאַחֲרָיוּתָן. וְהוּא הַדִּין לִדְבָרִים הַנִּמְכָּרִים לִרְפוּאָה וְלִצְבִיעָה. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
2.
If, by contrast, a seller sold seeds that are eaten - e.g., wheat or barley -and the purchaser sowed them, and they did not grow, the seller is not responsible to reimburse the purchaser.Even if he sold him flax seeds, which most people purchase to sow, the seller is not responsible if they are destroyed when they are sown, since there are some who eat these seeds.
If, however, the purchaser notifies the seller that he is purchasing the seeds with the intent of sowing them, the seller is responsible for them. The same applies to objects that are purchased for medicinal purposes or for dyes. Similar principles apply in all analogous situations.

הלכה ג
מִכָּאן אַתָּה לָמֵד שֶׁכָּל הַלּוֹקֵחַ מֵחֲבֵרוֹ מִקָּח וְהוֹדִיעוֹ שֶׁהוּא מוֹלִיכוֹ לִמְדִינָה פְּלוֹנִית לְמָכְרוֹ שָׁם וְאַחַר שֶׁהוֹלִיכוֹ לְשָׁם נִמְצָא בּוֹ מוּם. אֵינוֹ יָכוֹל לוֹמַר הַחֲזִיר לִי מִקָּחִי לְכָאן. אֶלָּא מַחְזִיר לוֹ אֶת הַדָּמִים וְהַמּוֹכֵר מְטַפֵּל לְהָבִיא מִמְכָּרוֹ אוֹ לְמָכְרוֹ שָׁם. וַאֲפִלּוּ אָבַד אוֹ נִגְנַב אַחַר שֶׁהוֹדִיעוֹ הֲרֵי הוּא בִּרְשׁוּת מוֹכֵר. אֲבָל אִם לֹא הוֹדִיעוֹ שֶׁמּוֹלִיכוֹ לִמְדִינָה אַחֶרֶת וְהוֹלִיכוֹ וְנִמְצָא שָׁם בּוֹ מוּם הֲרֵי זֶה בִּרְשׁוּת לוֹקֵחַ עַד שֶׁיַּחְזִיר הַמִּקָּח בְּמוּמוֹ לַמּוֹכֵר:
כסף משנה
3.
From the above, we can derive the following law. Whenever a person purchases an item from a colleague and informs him that he intends to transport it to another city to sell it there, and after he transported it there a blemish which nullifies the sale was discovered, the seller may not tell the purchaser: "Bring my article here." Instead, the seller must reimburse the purchaser, and the seller must take the trouble of returning the article to its original place or selling it in the place to which it was transported. Even if the article was lost or stolen after the purchaser notified the seller, it is considered to have been in the seller's domain.
Different laws apply, however, when the purchaser did not tell the seller that he was planning to transport the article to another country and transported it nevertheless. If he then discovered a blemish, the article is considered to be in the domain of the purchaser until he returns it with its blemish to the seller.

הלכה ד
הַלּוֹקֵחַ מִקָּח וְנִמְצָא בּוֹ מוּם וְאַחַר כָּךְ אָבַד אוֹ נִגְנַב הֲרֵי הוּא בִּרְשׁוּת הַלּוֹקֵחַ עַד שֶׁיַּחְזִיר הַמִּקָּח לַמּוֹכֵר. וְאִם הִתְלִיעַ וְנִפְסַד מֵחֲמַת אֹרֶךְ הַזְּמַן הֲרֵי זֶה בִּרְשׁוּת הַמּוֹכֵר. וְאִם הָיָה לוֹ לְהוֹדִיעַ לַמּוֹכֵר וְלֹא הוֹדִיעוֹ הֲרֵי זֶה בִּרְשׁוּת לוֹקֵחַ:
כסף משנה
4.
When a person purchases produce and discovers a blemish, and afterwards the article is lost or stolen, the article is considered in the domain of the purchaser until he returns it to the seller. If the produce becomes wormy and is spoiled because-of the length of time it had been kept, it is considered to be in the domain of the seller. If the purchaser realized the difficulty and should have notified the seller, but failed to do so, the produce is considered to be in his domain.

הלכה ה
הַמּוֹכֵר שׁוֹר לַחֲבֵרוֹ וְנִמְצָא נַגְחָן יָכוֹל לוֹמַר לוֹ לִשְׁחִיטָה מְכַרְתִּיו לְךָ. בַּמֶּה דְּבָרִים אֲמוּרִים בְּשֶׁהָיָה הַלּוֹקֵחַ קוֹנֶה לִשְׁחִיטָה וְלַחֲרִישָׁה. אֲבָל אִם הָיָה יוֹדֵעַ שֶׁהוּא קוֹנֶה לַחֲרִישָׁה בִּלְבַד הֲרֵי זֶה מִקַּח טָעוּת וְחוֹזֵר. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
5.
When a person sells an ox to a colleague and it is discovered to have tendencies to gore, the seller can excuse himself from responsibility by saying: "I sold it to you for the purpose of slaughter."When does the above apply? When the purchaser buys oxen for both slaughter and plowing. If, however, the seller knows that the purchaser purchases oxen only to plow, the transaction is considered to have been conducted under false premises, and it is nullified. The same principles apply in all analogous situations.

הלכה ו
הַמּוֹכֵר בְּהֵמָה לַחֲבֵרוֹ לִטְבִיחָה וּשְׁחָטָהּ וְנִמְצֵאת טְרֵפָה. אִם נוֹדַע בְּוַדַּאי שֶׁהָיְתָה טְרֵפָה כְּשֶׁלְּקָחָהּ הֲרֵי זֶה מַחְזִיר לוֹ אֶת הַשְּׁחוּטָה וְיַחְזִיר הַמּוֹכֵר אֶת הַדָּמִים. מִכָּאן אַתָּה לָמֵד שֶׁהַמּוֹכֵר דָּבָר שֶׁהָיָה מוּם בְּמִמְכָּרוֹ וְעָשָׂה בּוֹ הַלּוֹקֵחַ מוּם אַחֵר קֹדֶם שֶׁיִּוָּדַע לוֹ הַמּוּם הָרִאשׁוֹן. אִם עָשָׂה דָּבָר שֶׁדַּרְכּוֹ לַעֲשׂוֹתוֹ כְּגוֹן זֶה שֶׁשָּׁחַט אֶת הַטְּרֵפָה פָּטוּר. וְאִם שָׁנָה וְעָשָׂה מוּם אַחֵר קֹדֶם שֶׁיִּוָּדַע לוֹ הַמּוּם [הָרִאשׁוֹן] מַחְזִיר הַמִּקָּח לִבְעָלָיו וּמְשַׁלֵּם דְּמֵי הַמּוּם שֶׁעָשָׂה:
כסף משנה
6.
The following rule applies when a person sells an animal to a colleague for slaughter, the purchaser slaughters it, and it is discovered to be trefah. If it can definitely be determined that it had been trefah when it was purchased,the purchaser should return the slaughtered animal, and the seller must return the money.
From this ruling, we can derive the following principles that apply when a seller sells an entity that possesses a blemish, and the purchaser makes another blemish before he discovers the first blemish. If the purchaser creates the blemish in the process of performing an act that would ordinarily be performed - e.g., one who slaughters an animal that is trefah - he is not liable. If, however, he deviates from ordinary practice and makes another blemish before he discovers the first blemish, he should return the article to its owner and reimburse him for the blemish that he made.

הלכה ז
קָנָה בֶּגֶד וּקְרָעוֹ לַעֲשׂוֹת מִמֶּנּוּ חָלוּק וְאַחַר כָּךְ נוֹדַע הַמּוּם מֵחֲמַת הַקְּרִיעָה מַחְזִיר לוֹ אֶת הַקְּרָעִים. תְּפָרוֹ וְאַחַר כָּךְ נוֹדַע הַמּוּם. אִם הִשְׁבִּיחַ נוֹטֵל שֶׁבַח הַתְּפִירָה מִן הַמּוֹכֵר. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
7.
The following rules apply when a person purchases a garment and cuts it with the intent of making a cloak from it. If, because of the cut he made, he discovers a blemish in the fabric, he may return the pieces.
Should he sew the cloak and then discover the blemish in the fabric, he may return it. If he has increased its value, he may collect from the seller the value of the increase his sewing generated. Similar principles apply in all analogous situations.

הלכה ח
הַמּוֹכֵר קַרְקַע לַחֲבֵרוֹ וְאָכַל פֵּרוֹתֶיהָ וּלְאַחַר זְמַן נִרְאֶה לוֹ בָּהּ מוּם. אִם רָצָה לְהַחְזִיר קַרְקַע לַבְּעָלִים מַחְזִיר כָּל הַפֵּרוֹת שֶׁאָכַל. וְאִם הָיָה חָצֵר וְדָר בּוֹ צָרִיךְ לְהַעֲלוֹת לוֹ שָׂכָר:
כסף משנה
8.
The following principles apply when a person sells landed property to a colleague, the purchaser derives benefit from the property, and afterwards discovers a blemish in it. If he desires to return the land to its owners, he must reimburse them for all the benefit that he derived. If it was a courtyard and he dwelled in it, he must pay them rent.

הלכה ט
הַמּוֹכֵר דָּבָר שֶׁיֵּשׁ בּוֹ מוּם שֶׁאֵינוֹ נִרְאֶה וְאָבַד הַמִּקָּח מֵחֲמַת אוֹתוֹ הַמּוּם הֲרֵי זֶה מַחְזִיר אֶת הַדָּמִים:
כסף משנה
9.
When a person sells an article with a blemish that is not recognized, and the article that is sold becomes destroyed because of that blemish, the seller must return the money that he received.

הלכה י
[כֵּיצַד]. הַמּוֹכֵר שׁוֹר לַחֲבֵרוֹ שֶׁאֵין לוֹ טוֹחֲנוֹת וְהִנִּיחוֹ הַלּוֹקֵחַ עִם הַבָּקָר שֶׁלּוֹ וְהָיָה מַנִּיחַ הַמַּאֲכָל לִפְנֵי כֻּלָּן וְאוֹכְלִין וְלֹא הָיָה יוֹדֵעַ שֶׁזֶּה אֵינוֹ אוֹכֵל עַד שֶׁמֵּת בָּרָעָב. הֲרֵי זֶה מַחְזִיר לוֹ אֶת הַנְּבֵלָה וְיַחְזִיר זֶה אֶת הַדָּמִים. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
10.
What is implied? A person sold an ox that did not have molars. The purchaser placed that ox together with his cattle, placed food before all of them, and they ate. He did not realize that the ox he had purchased was not eating until it died of starvation.
In such an instance, the purchaser may return the corpse to the seller, who is required to return his money to him. Similar principles apply in all analogous situations.

הלכה יא
הָיָה הַמּוֹכֵר סַרְסוּר שֶׁלּוֹקֵחַ מִזֶּה וּמוֹכֵר לָזֶה וְאֵינוֹ מַשְׁהֶה הַמִּקָּח עִמּוֹ וְלֹא יָדַע בְּמוּם זֶה. הֲרֵי הַסַּרְסוּר נִשְׁבָּע שְׁבוּעַת הֶסֵּת שֶׁלֹּא יָדַע בְּמוּם זֶה וְיִפָּטֵר. מִפְּנֵי שֶׁהָיָה עַל הַלּוֹקֵחַ לִבְדֹּק הַשּׁוֹר בִּפְנֵי עַצְמוֹ וּלְהַחְזִירוֹ לוֹ קֹדֶם שֶׁיָּמוּת וְיִהְיֶה הַסַּרְסוּר מַחְזִירוֹ עַל הַמּוֹכֵר הָרִאשׁוֹן. הוֹאִיל וְלֹא עָשָׂה הוּא הַלּוֹקֵחַ הִפְסִיד עַל עַצְמוֹ. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
11.
Different rules apply if the seller is a broker who purchases from one person and sells to another without keeping the animal in his possession. For this reason, we assume that the broker did not know of the blemish. Therefore, the broker is required to take a Rabbinic oath that he did not know of the blemish, and then he is absolved of responsibility.
The rationale is that the purchaser had the responsibility of checking the ox he purchased independently and returning it to the broker before it died. The broker would then have returned it to the one who sold it to him. Since the purchaser did not do this, he caused himself a loss. Similar principles apply in all analogous situations.

הלכה יב
הַשּׁוֹחֵט אֶת הַבְּכוֹר וּמְכָרוֹ וְנוֹדַע לוֹ שֶׁלֹּא הֶרְאָהוּ לְמֻמְחֶה מַה שֶּׁאָכַל אָכַל וְיַחְזִיר לוֹ הַדָּמִים. וְהַנִּשְׁאָר מִן הַבָּשָׂר בְּיַד הַלָּקוֹחוֹת יְקַבֵּל וְיַחְזִיר לָהֶם אֶת הַדָּמִים. וְכֵן הַשּׁוֹחֵט אֶת הַפָּרָה וּמְכָרָהּ וְנוֹדַע שֶׁהִיא טְרֵפָה. מַה שֶּׁאָכַל אָכַל וְיַחְזִיר לוֹ אֶת הַדָּמִים וּמַה שֶּׁלֹּא אָכַל יַחְזִיר אֶת הַבָּשָׂר לַטַּבָּח וְיַחְזִיר לוֹ אֶת הַדָּמִים:
כסף משנה
12.
The following rules apply when a person slaughters a firstborn animal, sells its meat, and then the purchaser discovers that the seller had not shown it to an expert: What the purchaser ate is not taken into consideration, and the seller is required to return to the purchaser the money he paid. The seller should receive the remainder of the meat from the purchaser and return his money to him.
Similarly, if a butcher slaughters a cow and sells it, and it is discovered that it was trefah, what the purchaser ate is not taken into consideration, and the seller is required to return the purchaser's money to him.The meat that was not eaten should be returned to the butcher, ] and he should return the money to the purchaser.

הלכה יג
מָכַר הַלּוֹקֵחַ בָּשָׂר זֶה שֶׁל טְרֵפָה לְנָכְרִים. אוֹ שֶׁהֶאֱכִילוֹ לַכְּלָבִים. יְחַשֵּׁב עִם הַטַּבָּח עַל דְּמֵי הַטְּרֵפָה וְיַחְזִיר לוֹ הַטַּבָּח אֶת הַמּוֹתָר. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
13.
If the purchaser sold the meat that was trefah to gentiles, he should come to an understanding with the butcher with regard to the money for the trefah; the butcher should then return the remainder to him. Similar principles apply in all analogous situations.

הלכה יד
הַמּוֹכֵר בָּשָׂר לַחֲבֵרוֹ וְנִמְצָא בְּשַׂר בְּכוֹר. פֵּרוֹת וְנִמְצְאוּ טְבָלִים. יַיִן וְנִמְצָא יֵין נֶסֶךְ. מַה שֶּׁאָכַל אָכַל וְיַחְזִיר לוֹ אֶת הַדָּמִים. וְכֵן כָּל הַמּוֹכֵר דָּבָר שֶׁאָסוּר לְאָכְלוֹ מִן הַתּוֹרָה כָּךְ הוּא דִּינוֹ. בֵּין שֶׁהָיָה אִסּוּרוֹ בְּכָרֵת בֵּין שֶׁהָיָה אִסּוּרוֹ בְּלָאו בִּלְבַד. אֲבָל הַמּוֹכֵר דָּבָר לַחֲבֵרוֹ שֶׁאִסּוּר אֲכִילָתוֹ מִדִּבְרֵי סוֹפְרִים. אִם הָיוּ הַפֵּרוֹת קַיָּמִין מַחְזִיר אֶת הַפֵּרוֹת וְנוֹטֵל אֶת דָּמָיו. וְאִם אֲכָלָן אָכַל וְאֵין הַמּוֹכֵר מַחְזִיר לוֹ כְּלוּם. וְכָל אִסּוּרֵי הֲנָיָה בֵּין מִדִּבְרֵי תּוֹרָה בֵּין מִדִּבְרֵיהֶם מַחְזִיר אֶת הַדָּמִים וְאֵין בָּהֶן דִּין מְכִירָה כְּלָל:
כסף משנה
14.
When a person sells meat to a colleague and it is discovered to be the meat of a firstborn animal, or he sells produce and it is discovered to be tevel, or wine and it is discovered to be wine used for idolatry, what the purchaser consumed is not taken into consideration, and the seller is required to return the money he paid to the purchaser.
The same laws apply to any substance from which it is forbidden to partake according to Scriptural Law. This applies both when the prohibition is punishable by karet, or when there is merely an ordinary prohibition involved.
Different rules apply if one sells an object that is forbidden by Rabbinic law to be eaten. If the produce exists, one should return the produce and receive in return the money originally paid. If, however, one ate them, then one has benefited from it, and the seller is not obligated to return anything to the purchaser.
Whenever it is forbidden to benefit from an object - whether by Scriptural or Rabbinic law - the seller must return the money he received.There is no binding legal convention governing such a sale.

קניין הלכות מכירה פרק טז
Kinyan Mechirah Chapter 16