Halacha

הלכה א
מִי שֶׁאֵינוֹ לֹא בְּמִקְרָא וְלֹא בְּמִשְׁנָה וְלֹא בְּדֶרֶךְ אֶרֶץ הֲרֵי זֶה בְּחֶזְקַת רָשָׁע וּפָסוּל לְעֵדוּת מִדִּבְרֵיהֶם. שֶׁכָּל מִי שֶׁיָּרַד עַד כָּךְ חֲזָקָה שֶׁהוּא עוֹבֵר עַל רֹב הָעֲבֵרוֹת שֶׁיָּבוֹאוּ לְיָדוֹ:
כסף משנה
1.
When one does not read the Written Law, nor study the Oral Law, nor carry on ordinary social relationships, he can be assumed to be wicked and is disqualified as a witness according to Rabbinic decree. The rationale is that whenever a person has descended to such a degree, it can be assumed that he will transgress most transgressions that will present themselves to him.

הלכה ב
לְפִיכָךְ אֵין מוֹסְרִין עֵדוּת לְעַם הָאָרֶץ וְאֵין מְקַבְּלִין מִמֶּנּוּ עֵדוּת אֶלָּא אִם כֵּן הֻחְזַק שֶׁהוּא עוֹסֵק בְּמִצְוֹת וּבִגְמִילוּת חֲסָדִים וְנוֹהֵג בְּדַרְכֵי הַיְשָׁרִים וְיֵשׁ בּוֹ דֶּרֶךְ אֶרֶץ מְקַבְּלִין עֵדוּתוֹ אַף עַל פִּי שֶׁהוּא עַם הָאָרֶץ וְאֵינוֹ לֹא בְּמִקְרָא וְלֹא בְּמִשְׁנָה:
כסף משנה
2.
For this reason, unlearned people should not be designated as witnesses, nor do we accept such a person's testimony unless it has been established that he observes the mitzvot, performs acts of kindness, conducts himself in an upright manner, and carries on normal social relationships. The testimony of such a person may be accepted even though he is unlearned and is unfamiliar with both the Written and Oral Law.

הלכה ג
נִמְצֵאתָ אוֹמֵר כָּל תַּלְמִיד חָכָם בְּחֶזְקַת כָּשֵׁר עַד שֶׁיִּפָּסֵל. כָּל עַם הָאָרֶץ בְּחֶזְקַת שֶׁהוּא פָּסוּל עַד שֶׁיֻּחְזַק שֶׁהוּא הוֹלֵךְ בְּדַרְכֵי הַיְשָׁרִים:
כסף משנה
3.
Thus one may conclude any Torah scholar may be assumed to be acceptable as a witness unless he is disqualified, and any unlearned person may be assumed to be unacceptable unless it is established that he follows just paths.

הלכה ד
וְכָל מִי שֶׁיְּקַבֵּל עֵדוּת עַם הָאָרֶץ טֶרֶם שֶׁתִּהְיֶה לוֹ חֲזָקָה זוֹ אוֹ קֹדֶם שֶׁיָּבוֹאוּ עֵדִים וְיָעִידוּ שֶׁהוּא נוֹהֵג בְּמִצְוֹת וּבְדֶרֶךְ אֶרֶץ הֲרֵי זֶה הֶדְיוֹט וְעָתִיד לִתֵּן אֶת הַדִּין שֶׁהֲרֵי מְאַבֵּד מָמוֹנָן שֶׁל יִשְׂרָאֵל עַל פִּי רְשָׁעִים:
כסף משנה
4.
Whoever accepts the testimony of an unlearned person before it is established that he possesses the above positive qualities or before witnesses come and testify that he observes the mitzvot and carries on ordinary social relations is a commoner and will be required to face judgment, for he has forfeited the financial resources of Jews on the basis of the testimony of the wicked.

הלכה ה
וְכֵן הַבְּזוּיִין פְּסוּלִין לְעֵדוּת מִדִּבְרֵיהֶם וְהֵם הָאֲנָשִׁים שֶׁהוֹלְכִין וְאוֹכְלִין בַּשּׁוּק בִּפְנֵי כָּל הָעָם וּכְגוֹן אֵלּוּ שֶׁהוֹלְכִין עֲרוּמִים בַּשּׁוּק בְּעֵת שֶׁהֵן עוֹסְקִין בִּמְלָאכָה מְנֻוֶלֶת וְכַיּוֹצֵא בְּאֵלּוּ שֶׁאֵין מַקְפִּידִין עַל הַבּשֶׁת. שֶׁכָּל אֵלּוּ חֲשׁוּבִין כְּכֶלֶב וְאֵין מַקְפִּידִין עַל עֵדוּת שֶׁקֶר. וּמִכְּלַל אֵלּוּ הָאוֹכְלִין צְדָקָה שֶׁל עַכּוּ''ם בְּפַרְהֶסְיָא אַף עַל פִּי שֶׁאֶפְשָׁר לָהֶן שֶׁיִּזּוֹנוּ בְּצִנְעָה מְבַזִּים עַצְמָן וְאֵינָן חוֹשְׁשִׁין. כָּל אֵלּוּ פְּסוּלִין מִדִּבְרֵיהֶם:
כסף משנה
5.
Similarly, base people are disqualified as witnesses by Rabbinic decree. This refers to people who walk through the marketplace eating in the presence of everyone, those who go unclothed in the marketplace when they are involved in ignoble tasks, and the like. The rationale is that they are not concerned with their own shame. All these people are considered as dogs; they will not be concerned with testifying falsely.
Included are those who partake of charity given by gentiles in public. Although they could derive this benefit in private, they denigrate themselves and accept it in public without showing concern for their honor. All of these individuals are disqualified according to Rabbinical decree.

הלכה ו
מַה בֵּין פָּסוּל לְעֵדוּת מִן הַתּוֹרָה לְפָסוּל מִדִּבְרֵיהֶם. שֶׁהַפָּסוּל מִן הַתּוֹרָה שֶׁהֵעִיד עֵדוּתוֹ בְּטֵלָה אַף עַל פִּי שֶׁלֹּא הִכְרִיזוּ עָלָיו בְּבָתֵּי כְּנֵסִיּוֹת וּבְבָתֵּי מִדְרָשׁוֹת וְהַפָּסוּל מִדִּבְרֵיהֶם צָרִיךְ הַכְרָזָה. לְפִיכָךְ כָּל עֵדוּת שֶׁהֵעִיד קֹדֶם שֶׁהִכְרִיזוּ עָלָיו מְקַבְּלִין אוֹתָה כְּדֵי שֶׁלֹּא לְאַבֵּד זְכוּת הָעָם שֶׁהֲרֵי לֹא יָדְעוּ שֶׁהוּא פָּסוּל וְאֵין פְּסוּלוֹ אֶלָּא מִדִּבְרֵיהֶם:
כסף משנה
6.
What is the difference between a person who is disqualified as a witness according to Scriptural Law and one who is disqualified by Rabbinic decree? The testimony of a person disqualified by Scriptural Law is nullified even though it was not announced in synagogues and houses of study that he is unacceptable.
Announcements must be made about a person who is disqualified by Rabbinic decree, by contrast, before his testimony is disqualified. Accordingly, any testimony that he gives before such announcements are made are accepted so that people who relied on him will not suffer a loss, for they did not know that he was unacceptable, and he is disqualified only by Rabbinic decree.

הלכה ז
עֵד אֶחָד נֶאֱמָן בְּאִסּוּרִין אַף עַל פִּי שֶׁהוּא פָּסוּל לִשְׁאָר עֵדוּיוֹת. שֶׁהֲרֵי רָשָׁע בַּעֲבֵרָה שֶׁשָּׁחַט שְׁחִיטָתוֹ כְּשֵׁרָה וְנֶאֱמָן לוֹמַר כַּהֲלָכָה שָׁחַטְתִּי. אֲבָל הֶחָשׁוּד עַל דָּבָר אֵינוֹ נֶאֱמָן עַל שֶׁלּוֹ אֲבָל נֶאֱמָן הוּא עַל אֲחֵרִים:
כסף משנה
7.
The testimony of one witness is acceptable with regard to the Torah's prohibitions, even though his testimony is not accepted with regard to other matters. This is evident from the fact that when a wicked person known to transgress slaughters an animal, his slaughter is acceptable. We accept his word when he says: "I slaughtered it according to law." When, however, a person is suspected of violating a particular prohibition frequently, his word is not accepted with regard to his own matters. His word is accepted, however, with regard to others.

הלכה ח
לְפִיכָךְ הֶחָשׁוּד עַל דָּבָר יֵשׁ לוֹ לָדוּן בּוֹ וּלְהָעִיד בּוֹ לַאֲחֵרִים. חֲזָקָה אֵין אָדָם חוֹטֵא כְּדֵי שֶׁיֵּהָנוּ אֲחֵרִים. כֵּיצַד. נֶאֱמָן עַם הָאָרֶץ לוֹמַר פֵּרוֹת פְּלוֹנִי מְתֻקָּנִים הֵם. וְנֶאֱמָן הַנֶּחְשָׁד לִמְכֹּר בְּשַׂר בְּכוֹר לוֹמַר בָּשָׂר זֶה שֶׁמּוֹכֵר פְּלוֹנִי חֻלִּין הוּא. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה מִשְּׁאָר הָאִסּוּרִין. לְפִי שֶׁאֵימַת הָאִסּוּרִים עַל הָרְשָׁעִים וְאֵין אֵימַת הַמָּמוֹן עֲלֵיהֶן:
כסף משנה
8.
For this reason, a person suspected of violating a particular prohibition may serve as a judge and as a witness for others. We operate under the assumption that a person will not transgress so that others will benefit.
What is implied? The word of an unlearned person is accepted if he states: "The produce of so-and-so has been tithed." Similarly, the word of a person who is suspected of selling the meat of a firstborn is accepted if he states: "The meat which so-and-so is selling is ordinary meat." Similar principles apply with regard to other prohibitions. For the wicked fear the Torah's prohibitions, but they do not fear causing others monetary loss.

הלכה ט
מַלְכֵי יִשְׂרָאֵל לֹא מְעִידִין וְלֹא מְעִידִין עֲלֵיהֶן מִפְּנֵי שֶׁהֵן אַלָּמִים בַּעֲלֵי זְרוֹעַ וְאֵינָן נִכְנָעִין תַּחַת עֹל הַדַּיָּנִים. אֲבָל כֹּהֵן גָּדוֹל מְעִידִין עָלָיו וּמֵעִיד הוּא לַמֶּלֶךְ בְּבֵית דִּין הַגָּדוֹל כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
9.
The Kings of Israel may not testify, nor is testimony given against them, because they are strong-armed men of power who do not subjugate themselves to the yoke of the judges. Testimony may be made against a High Priest, by contrast, and he may give testimony concerning the king in the Supreme Sanhedrin, as explained.

הלכה י
הַמּוֹסְרִין וְהָאֶפִּיקוֹרוֹסִין וְהַמּוּמָרִים לֹא הִצְרִיכוּ חֲכָמִים לִמְנוֹתָן בִּכְלַל פְּסוּלֵי עֵדוּת שֶׁלֹּא מָנוּ אֶלָּא רִשְׁעֵי יִשְׂרָאֵל. אֲבָל אֵלּוּ הַמּוֹרְדִין הַכּוֹפְרִין פְּחוּתִין הֵן מִן הָעַכּוּ''ם. שֶׁהָעַכּוּ''ם לֹא מַעֲלִין וְלֹא מוֹרִידִין וְיֵשׁ לַחֲסִידֵיהֶן חֵלֶק לָעוֹלָם הַבָּא. וְאֵלּוּ מוֹרִידִין וְלֹא מַעֲלִין וְאֵין לָהֶן חֵלֶק לָעוֹלָם הַבָּא:
כסף משנה
10.
Our Sages had no need to list informers, epicursim, and apostates among those who are not acceptable as witnesses. For they listed only the wicked among the Jewish people. These rebellious deserters of the faith are inferior to the gentiles. Gentiles need not be saved from a pit, but neither should they be pushed into one the pious among them will receive a share in the world to come. These deserters of the faith should be pushed into a pit and should not be saved from one; they will not receive a portion in the world to come.

שופטים הלכות עדות פרק יא
Shoftim Edus Chapter 11