Halacha

הלכה א
הַמַּלְוֶה אֶת חֲבֵרוֹ עַל הַמַּשְׁכּוֹן בֵּין שֶׁהִלְוָהוּ מָעוֹת בֵּין שֶׁהִלְוָהוּ פֵּרוֹת בֵּין שֶׁמִּשְׁכְּנוֹ בִּשְׁעַת הַלְוָאָתוֹ בֵּין שֶׁמִּשְׁכְּנוֹ אַחַר שֶׁהִלְוָהוּ הֲרֵי זֶה שׁוֹמֵר שָׂכָר. לְפִיכָךְ אִם אָבַד הַמַּשְׁכּוֹן אוֹ נִגְנַב חַיָּב בְּדָמָיו. וְאִם נֶאֱנַס הַמַּשְׁכּוֹן כְּגוֹן שֶׁנִּלְקַח בְּלִסְטִים מְזֻיָּן וְכַיּוֹצֵא בּוֹ מִשְּׁאָר אֳנָסִין יִשָּׁבַע שֶׁנֶּאֱנַס וִישַׁלֵּם בַּעַל הַמַּשְׁכּוֹן אֶת חוֹבוֹ עַד פְּרוּטָה אַחֲרוֹנָה:
כסף משנה
1.
The following rules apply when a person gives a loan to a colleague and takes security in return. He is considered to be a paid watchman. This applies regardless of whether he lent him money or lent him produce, and regardless of whether he took the security at the time when he gave him the loan or afterwards.
Accordingly, if the security is lost or stolen, he is responsible for its value. If the security was lost because of causes beyond the lender's control -e.g., it was taken by armed thieves or the like - the lender must take an oath that it was lost due to forces beyond his control, and the owner of the security must repay his debt until the last p'rutah.

הלכה ב
כָּל הָאוֹמֵר לַחֲבֵרוֹ שְׁמֹר לִי וְאֶשְׁמֹר לְךָ הֲרֵי זֶה שְׁמִירָה בַּבְּעָלִים. אָמַר לוֹ שְׁמֹר לִי הַיּוֹם וְאֶשְׁמֹר לְךָ לְמָחָר. הַשְׁאִילֵנִי הַיּוֹם וַאֲנִי אַשְׁאִילְךָ לְמָחָר. שְׁמֹר לִי הַיּוֹם וְאַשְׁאִילְךָ לְמָחָר. הַשְׁאִילֵנִי הַיּוֹם וְאֶשְׁמֹר לְךָ לְמָחָר. כֻּלָּן נַעֲשׂוּ שׁוֹמְרֵי שָׂכָר זֶה לָזֶה:
כסף משנה
2.
Whenever a person tells a colleague: "Watch my article for me and I will watch your article for you," it is considered as if the owner was employed by the watchman.
If, however, he tells his colleague: "Watch an article for me today, and I will watch an article for you tomorrow," "Lend an article to me today and I will lend an article to you tomorrow," "Watch an article for me today, and I will lend an article to you tomorrow," or "Lend an article to me today and I will watch an article for you tomorrow," they are each considered to be paid watchman for the other.

הלכה ג
כָּל הָאֻמָּנִין שׁוֹמְרֵי שָׂכָר הֵן. וְכֻלָּן שֶׁאָמְרוּ טל אֶת שֶׁלְּךָ וְהָבֵא מָעוֹת אוֹ שֶׁאוֹמֵר לוֹ הָאֻמָּן גְּמַרְתִּיו וְלֹא לָקְחוּ הַבְּעָלִים אֶת הַכְּלִי הָאֻמָּן שׁוֹמֵר חִנָּם. אֲבָל אִם אָמַר הָאֻמָּן הָבֵא מָעוֹת וְטל שֶׁלְּךָ עֲדַיִן הוּא נוֹשֵׂא שָׂכָר כְּשֶׁהָיָה:
כסף משנה
3.
All craftsmen are considered to be paid watchman. Whenever a craftsman says: "Take your article and pay for it," or "I have completed it," and the owner does not take the article, the craftsman is considered to be an unpaid watchman from that time onward.
If, however, the craftsman says: "Bring money and take your article," he is considered a paid watchman as before.

הלכה ד
נָתַן לְאֻמָּנִין לְתַקֵּן וְקִלְקְלוּ חַיָּבִין לְשַׁלֵּם. כֵּיצַד. נָתַן לְחֵרֵשׁ שִׁדָּה תֵּבָה וּמִגְדָּל לִקְבֹּעַ בָּהֶן מַסְמֵר וּשְׁבָרוֹ אוֹ שֶׁנָּתַן לוֹ אֶת הָעֵצִים לַעֲשׂוֹת מֵהֶן שִׁדָּה תֵּבָה וּמִגְדָּל וְנִשְׁבְּרוּ אַחַר שֶׁנַּעֲשׂוּ מְשַׁלֵּם לוֹ דְּמֵי שִׁדָּה תֵּבָה וּמִגְדָּל. שֶׁאֵין הָאֻמָּן קוֹנֶה בְּשֶׁבַח הַכְּלִי. נָתַן צֶמֶר לְצַבָּע וְהִקְדִיחַתּוּ יוֹרָה נוֹתֵן לוֹ דְּמֵי צִמְרוֹ. צְבָעוֹ כָּעוּר אוֹ נְתָנוֹ לוֹ לְצָבְעוֹ אָדֹם וּצְבָעוֹ שָׁחוֹר שָׁחוֹר וּצְבָעוֹ אָדֹם. נָתַן עֵצִים לְחָרָשׁ לַעֲשׂוֹת מֵהֶן כִּסֵּא נָאֶה וְעָשָׂה כִּסֵּא רַע אוֹ סַפְסָל. אִם הַשֶּׁבַח יָתֵר עַל הַהוֹצָאָה נוֹתֵן בַּעַל הַכְּלִי אֶת הַהוֹצָאָה וְאִם הַהוֹצָאָה יְתֵרָה עַל הַשֶּׁבַח נוֹתֵן לוֹ אֶת הַשֶּׁבַח בִּלְבַד. אָמַר בַּעַל הַכְּלִי אֵינִי רוֹצֶה בְּתַקָּנָה זוֹ אֶלָּא יִתֵּן לִי דְּמֵי הַצֶּמֶר אוֹ דְּמֵי הָעֵצִים אֵין שׁוֹמְעִין לוֹ. וְכֵן אִם אָמַר הָאֻמָּן הֵא לְךָ דְּמֵי צִמְרְךָ אוֹ דְּמֵי עֵצְךָ וְלֵךְ אֵין שׁוֹמְעִין לוֹ שֶׁאֵין הָאֻמָּן קוֹנֶה בְּשֶׁבַח כְּלִי שֶׁעָשָׂה:
כסף משנה
4.
If a person gives an article to a craftsman to fix and the craftsman ruins it, the craftsman is liable to make restitution.
What is implied? If a person gives a carpenter a chest, a box or a closet to place a nail into, and he breaks the article he must make restitution. Similarly, if a person gives a carpenter the wood to make a chest, a box or a closet, and he breaks them after he completes making them, the carpenter must pay the employer for a chest, a box or a closet. The rationale is that the craftsman does not acquire a share in the increase in the value of the article.
If a person gives a craftsman wool to dye, and the vat in which he dyes it boils until the water evaporates, thus destroying the wool, the dyer must reimburse the owner for his wool.
The following rules apply in the ensuing situations: The dyer dyed the wool unattractively, the owner asked him to dye it red and he dyed it black, he asked him to dye it black and he dyed it red, or he gave wood to a carpenter to make an attractive chair, and he made a poor chair or a bench. In all these instances, if the increase in the value of the article exceeds the cost, all the owner of the article is required to pay is the cost. If the cost exceeds the increase in the value of the article, all the owner of the article is required to pay is the increase in the value of the article.
If the owner of the article says: "I do not desire this dispensation. I would prefer that he give me the value of the wool or the value of the wood," we do not heed his request. Conversely, if the craftsman says: "Here is the cost of your wool or your wood, depart," he is not heeded. The rationale is that the craftsman does not acquire a share in the increase in the value of the article.

הלכה ה
הַמּוֹלִיךְ חִטִּין לִטְחֹן וְלֹא לְתָתָן וַעֲשָׂאָן סֻבִּין אוֹ מֻרְסָן. נָתַן הַקֶּמַח לְנַחְתּוֹם וַעֲשָׂאוֹ פַּת נְפוֹלִין. בְּהֵמָה לְטַבָּח וְנִבְּלָהּ. חַיָּבִין לְשַׁלֵּם דְּמֵיהֶן מִפְּנֵי שֶׁהֵן נוֹשְׂאֵי שָׂכָר. לְפִיכָךְ אִם הָיָה טַבָּח מֻמְחֶה וְשָׁחַט בְּחִנָּם פָּטוּר מִלְּשַׁלֵּם וְאֵינוֹ מֻמְחֶה אַף עַל פִּי שֶׁהוּא בְּחִנָּם חַיָּב לְשַׁלֵּם. וְכֵן הַמַּרְאֶה דִּינָר לְשֻׁלְחָנִי וְאָמַר לוֹ יָפֶה הוּא וְנִמְצָא רַע אִם בְּשָׂכָר רָאָהוּ חַיָּב לְשַׁלֵּם אַף עַל פִּי שֶׁהוּא בָּקִי וְאֵינוֹ צָרִיךְ לְהִתְלַמֵּד. וְאִם בְּחִנָּם רָאָהוּ פָּטוּר וְהוּא שֶׁיִּהְיֶה בָּקִי שֶׁאֵינוֹ צָרִיךְ לְהִתְלַמֵּד. וְאִם אֵינוֹ בָּקִי חַיָּב לְשַׁלֵּם אַף עַל פִּי שֶׁהוּא בְּחִנָּם וְהוּא שֶׁיֹּאמַר לַשֻּׁלְחָנִי עָלֶיךָ אֲנִי סוֹמֵךְ אוֹ שֶׁהָיוּ הַדְּבָרִים מַרְאִין שֶׁהוּא סוֹמֵךְ עַל רְאִיָּתוֹ וְלֹא יַרְאֶה לַאֲחֵרִים. טַבָּח שֶׁעָשָׂה בְּחִנָּם וְנִבֵּל וְכֵן שֻׁלְחָנִי שֶׁאָמַר יָפֶה וְנִמְצָא רַע וְכֵן כָּל כַּיּוֹצֵא בָּזֶה עֲלֵיהֶן לְהָבִיא רְאָיָה שֶׁהֵן מֻמְחִין. וְאִם לֹא הֵבִיאוּ רְאָיָה מְשַׁלְּמִין:
כסף משנה
5.
When a person brings raw materials to a professional and he ruins them, the professional is liable to reimburse the owner for their value, for he is like a paid watchman. For example, a person gave wheat to a miller to grind and he did not soak it. Hence the flour came out as bran or coarse flour. A person gave flour to a baker and he made bread that crumbles, or a person brought an animal to a slaughterer and he slaughtered it unacceptably. They are all liable to make restitution.
Therefore, if an expert slaughterer slaughters an animal without charge and he caused it to be unacceptable, he is not liable to make restitution. If he is not an expert, even if he works without charge, he is required to make restitution.
Similar rules apply when a person shows a coin to a money changer and he says that it is acceptable, and it is discovered to be unacceptable. If he charged for his services, he is obligated to pay even though he is an expert and does not require further training. If he did not charge, he is not liable, provided he is an expert and does not require further training. If he is not an expert, he must reimburse the questioner even when he does not charge for his services.
The above applies when the questioner tells the money changer: "I am relying upon you," or it is obvious from the situation that he is relying on his opinion and is not seeking another opinion.
When a ritual slaughterer slaughtered an animal without charge, but rendered it unfit, a money changer said that a coin was acceptable, and it was not, or in any similar situation, the person who caused the damage must supply proof that he is an expert. If he cannot supply proof, he is required to make restitution.

הלכה ו
מָקוֹם שֶׁנָּהֲגוּ שֶׁיִּהְיֶה הַנּוֹטֵעַ אִילָנוֹת נוֹטֵל חֲצִי הַשֶּׁבַח וּבַעַל הַקַּרְקַע חֲצִי וְנָטַע וְהִשְׁבִּיחַ וְנָטַע וְהִפְסִיד מְחַשְּׁבִין לוֹ חֲצִי הַשֶּׁבַח שֶׁיֵּשׁ לוֹ וּמְנַכִּין מִמֶּנּוּ מַה שֶּׁהִפְסִיד וְנוֹטֵל הַשְּׁאָר. וַאֲפִלּוּ הִתְנָה עַל עַצְמוֹ שֶׁאִם הִפְסִיד לֹא יִטּל כְּלוּם הֲרֵי זֶה אַסְמַכְתָּא וְאֵין מְנַכִּין לוֹ אֶלָּא מַה שֶּׁהִפְסִיד. הָיָה מִנְהָגָם שֶׁיִּטּל הַנּוֹטֵעַ מֶחֱצָה וּבַעַל הַקַּרְקַע מֶחֱצָה וְכָךְ הָיָה מִנְהָגָם שֶׁיִּטּל הָאָרִיס שְׁלִישׁ. אִם נָטַע הַנּוֹטֵעַ וְהִשְׁבִּיחַ וְרָצָה לְהִסְתַּלֵּק שֶׁנִּמְצָא בַּעַל הַקַּרְקַע צָרִיךְ לְהוֹרִיד לָהּ אָרִיס הֲרֵי בַּעַל הַקַּרְקַע מוֹרִיד אָרִיס וְיִטּל בַּעַל הַקַּרְקַע חֶצְיוֹ וְלֹא יַפְסִיד בַּעַל הַקַּרְקַע כְּלוּם וְיִטּל הָאָרִיס שְׁלִישׁ וְהַשְּׁתוּת הַנִּשְׁאָר שֶׁל נוֹטֵעַ שֶׁהֲרֵי סִלֵּק עַצְמוֹ בִּרְצוֹנוֹ:
כסף משנה
6.
The following rules apply in a place where it is customary for a person who plants trees to receive half of the increase in value, and for the owner of the land to receive half of the increase in value. If he planted trees in a portion of the land and increased the value, but planted other trees in another portion of the land and caused a loss, we calculate the half of the profit that is due the planter and deduct the entire loss he caused. He then receives the remainder. Even if he stipulated that if he causes a loss in a certain portion of the land, he will not receive any profit at all, his words are not heeded and only the loss he actually caused is deducted from his profits. The rationale is that this stipulation is an asmachta.
When the person who plants trees terminates his relationship with the owner before reaping the crop, he bears the responsibility for his actions. To illustrate this principle: The local custom is that the person who plants receives half of the profits and the owner of the land, the other half. A sharecropper receives a lesser share, one third of the crop. The person who planted the trees caused the land to increase in value and then wished to terminate his relationship with the owner, forcing the owner to employ a sharecropper. The owner of the land may employ a sharecropper. Even so, the owner of the land receives half of the profits; he does not suffer a loss.
The sharecropper receives a third and the remaining sixth is given to the person who planted the trees. Since he willingly terminated his relationship, he suffers the consequences.

הלכה ז
הַנּוֹטֵעַ אִילָנוֹת לִבְנֵי הַמְּדִינָה שֶׁהִפְסִיד. וְכֵן טַבָּח שֶׁל בְּנֵי הָעִיר שֶׁנִּבֵּל הַבְּהֵמוֹת. וְהַמַּקִּיז דָּם שֶׁחָבַל. וְהַסּוֹפֵר שֶׁטָּעָה בִּשְׁטָרוֹת. וּמְלַמֵּד תִּינוֹקוֹת שֶׁפָּשַׁע בְּתִינוֹקוֹת וְלֹא לִמֵּד אוֹ לִמֵּד בְּטָעוּת. וְכָל כַּיּוֹצֵא בְּאֵלּוּ הָאֻמָּנִים שֶׁאִי אֶפְשָׁר שֶׁיַּחְזִירוּ הַהֶפְסֵד שֶׁהִפְסִידוּ. מְסַלְּקִין אוֹתָן בְּלֹא הַתְרָאָה שֶׁהֵן כְּמֻתְרִין וְעוֹמְדִין עַד שֶׁיִּשְׁתַּדְּלוּ בִּמְלַאכְתָּן הוֹאִיל וְהֶעֱמִידוּ אוֹתָן הַצִּבּוּר עֲלֵיהֶם:
כסף משנה
7.
The following principle applies with regard to a person who plants trees on behalf of all the members of a city who caused a loss; similarly, a ritual slaughterer of a village who rendered an animal unacceptable for consumption, a blood-letter who caused an injury, a scribe who erred in composing a legal document, a teacher who was negligent with the children and did not teach them or taught them in error, or any other professional who made an error that cannot be corrected. They may be removed from their positions without warning, for the warning for them to perform their work carefully is self evident. They must faithfully apply themselves to their tasks, for they were appointed by the community to discharge this responsibility.

משפטים הלכות שכירות פרק י
Mishpatim Schirus Chapter 10