Gemara

R. Yosi is concerned for ill will:

(Beraisa - R. Yosi): Everyone is believed about Taharah of wine and oil the entire year, lest everyone build his own Bamah and offer his own Parah Adumah on it.

(Rav Papa): Nowadays we accept testimony from an Am ha'Aretz. This is like R. Yosi.

Kidushin 40b (Mishnah): If one does not learn Torah or Mishnah, and has no Derech Eretz, he is not civilized.

(R. Yochanan): Such a person cannot be a witness.

(Beraisa): One who eats in the market is like a dog;

Some say, he cannot be a witness.

(Rav Idi bar Avin): The Halachah follows the latter opinion.

Pesachim 49b (Beraisa): Six laws were taught regarding an Am ha'Aretz:

We do not entrust testimony to him (ask him to witness something). We do not accept testimony from him. We do not reveal secrets to him. We do not make him an overseer over orphans or over Tzedakah. One may not accompany him on the road.

Sanhedrin 26b (Rav Nachman): Those who consume 'Devar Acher' (this will be explained) are disqualified from testifying.

This is only if they take in public. If they take privately, they are Kesherim. Even if they take in public, they are disqualified only if they could take privately but do not. If they have no choice but to take in public, this is their livelihood, they are Kesherim.

Yevamos 63b (Beraisa): "B'Goy Naval Ach'isem" - these are the people of Barberiya, and Martenai, who walk naked in the market. Nothing is more repulsive to Hash-m than such people.

Tana d'vei Eliyahu Zuta (16, Sof DH Ma'aseh): We do not appoint a bloodletter, bathhouse attendant or tanner (these are disgraceful professions) to a position of authority or to be an overseer of orphans,

R. Yosi disqualifies them from testimony.

Rishonim

Rif and Rosh (Pesachim 16a and 3:10): We do not entrust testimony to an Am ha'Aretz. We do not accept testimony from him;

Question (Rif): In Chagigah we learned that nowadays we accept testimony from an Am ha'Aretz, like R. Yosi!

Answer (Rif): That discusses one who does not learn Torah or Mishnah, but he fulfills Mitzvos and has Derech Eretz. He is not suspected to swear falsely, steal, or anything that disqualifies from testimony. Here (in Pesachim) we discuss one who is suspected of theft and murder, therefore we do not make him an overseer or accompany him on the road.

Rebuttal (Rosh, ibid.): What did the Rif find difficult? In Chagigah we say that he should be Pasul, but if we distance Amei ha'Aretz perhaps they will establish their own creed and Batei Dinim. Therefore, we accept their testimony, just like R. Yosi says that we rely on their Taharos lest they burn their own Parah Adumah! The Rif says that the Am ha'Aretz is not suspected of anything. If so, all agree that he may testify; we do not need special reasons! Rather, here we discuss an Am ha'Aretz suspected of Aveiros.

Ran (DH v'Ein): 'We do not accept testimony' connotes l'Chatchilah, but b'Di'eved, it is testimony. However, the Rif says that here we discuss a total Rasha, so he must say that even b'Di'eved the testimony is Pasul. He says that Rav Papa says that we accept testimony from an Am ha'Aretz who keeps Mitzvos and has Derech Eretz, like R. Yosi. No one disagrees! Indeed, sometimes the Gemara attributes a practice to a certain opinion even though no one argues. Rashi explains that both places discuss an Am ha'Aretz who keeps Mitzvos and has Derech Eretz. Chachamim say that l'Chatchilah we do not accept his testimony. Nowadays we accept it l'Chatchilah, like R. Yosi. This is better than the Rif's Perush.

Question: If we do not accept testimony from an Am ha'Aretz, there is no need to say that we do not Moser testimony to him (ask him to witness something)!

Answer #1 (Me'iri Chagigah 22a DH mi'Mah): The Rif holds that Pesachim discusses one who lacks even Derech Eretz. His testimony is Pasul even b'Di'eved. Even if he has Derech Eretz, l'Chatchilah we do not Moser testimony to him for he is not precise. Some say that if he testifies we require Drishah v'Chakirah (even though normally monetary cases do not).

Answer #2 (Me'iri Pesachim 49b DH Shishah): 'We do not Moser testimony to him' means that he may not make him part of a Beis Din.

Rif and Rosh (Sanhedrin 5a and 3:12): One who consumes 'Devar Acher', i.e. takes Tzedakah from Nochrim, is disqualified. This is only if he could take privately, but he takes in public and disgraces himself. If he has no alternative, he is Kosher.

Nimukei Yosef (DH Pesulim): He is Pasul because it is Chilul Hash-m. If he has no alternative he is Kosher, for this is "Va'Chai Bahem"!

Rif and Rosh (Kidushin 16a and 1:64): If one does not learn Torah or Mishnah and has no Derech Eretz, he is not civilized. He is Pasul for testimony.

Rif (ibid.): One who eats in the market is like a dog. Some say, he cannot be a witness. The Halachah follows this opinion.

Rambam (Hilchos Edus 11:1): If one does not learn Torah or Mishnah or have Derech Eretz, the Chazakah is that he is a Rasha. Mid'Rabanan, he is Pasul for testimony. One who has descended so low is Muchzak to transgress in most opportunities.

Rambam (2): Therefore, we do not entrust testimony to an Am ha'Aretz and we do not accept testimony from him unless he is Muchzak to engage in Mitzvos and Chesed, act properly and have Derech Eretz.

Rambam (5): Similarly, mid'Rabanan disgraceful people are Pasul for testimony. These are people who eat in the market in front of everyone, walk naked in the market when doing disgusting work, and similar things that show that they have no shame. All of these people are like dogs; they are not concerned about false testimony.

Question (Rosh Kidushin 1:65): In the Yerushalmi, R. Meir told R. Shimon b'Ribi that it is not proper for a Chacham to eat in the market. This implies that others may. Why does this disqualify from testimony?

Answers 1-3 (Rosh): R. Chananel says that he grabs from others and eats. We must say that he takes less than a Perutah's worth, or things that people do not care about, for otherwise he is disqualified due to burglary! R. Eliyahu says that he tastes from different vendors, pretending that he plans to buy. R. Tam says that he has a (bread) meal, which is more disgraceful.

Question (Einayim l'Mishpat Kidushin Sof 40b): Stealing less than a Shi'ur is like an Aveirah for which one is not lashed. In any case it is no less than an Aveirah mid'Rabanan, and these disqualify (Rema 34:2,3)!

Note: Perhaps people think that it is only Midas Chasidus to refrain from stealing less than a Perutah, so it does not disqualify.

Answer #4 (Bach CM 34 DH ha'Ochel): Rashi says that one who eats in the market, i.e. constantly, has no shame. A Chacham should not eat there even occasionally.

Poskim

Shulchan Aruch (CM 34:17): If one does not learn Torah or Mishnah or act properly, the Chazakah is that he is a Rasha. Mid'Rabanan, he is Pasul for testimony. Therefore, we do not entrust testimony to an Am ha'Aretz to be a witness and we do not accept testimony from him unless he is Muchzak to engage in Mitzvos and Chesed, and acts properly and has Derech Eretz.

Beis Yosef (DH u'Mah she'Chosav): It seems that the Rambam learns like the Rif. The Gemara in Pesachim discusses a Stam Am ha'Aretz, who lacks Derech Eretz. Chagigah discusses an Am ha'Aretz with Derech Eretz and Mitzvos. Since he does not learn, it would be fitting to disqualify him, if not, for R. Yosi's reason. The Rosh permits testimony even if the Am ha'Aretz has no Derech Eretz, like R. Yosi. This is unlike the Rambam.

Question: Why the Tur (who normally follows the Rosh) rule like the Rambam, without mentioning the Rosh's opinion?

Answer (Beis Yosef): The Tur holds that the Rosh does not rule like R. Yosi. Rav Papa did not mean that the Halachah follows R. Yosi. Rather, he teaches that according to R. Yosi we should accept Amei ha'Aretz. The Halachah follows the Beraisa in Pesachim, which says that we do not do so. The Mordechai says that one who is not zealous about Tefilah and Mitzvos and lacks Derech Eretz is Pasul. The Am ha'Aretz of Pesachim engages in Torah, Mitzvos and Derech Eretz, but he is not a Ben Torah.

Hagahos Drishah (8): Perhaps this is a textual error; it should say 'the Am ha'Aretz of Chagigah engages in Torah... Alternatively, it refers to the Am ha'Aretz of Pesachim. His testimony is valid b'Di'eved if he engages in Mitzvos...

Question: We say that he is Pasul only if he lacks all of these (learning, Mitzvos, Chesed, and acts properly with Derech Eretz), but we say that he is Kosher only if he has all of them!

Answer (SMA 42): If we know that someone learns and has Derech Eretz, even if we do not know whether or not he keeps Mitzvos, the Chazakah is that he does, therefore he is a Kosher witness l'Chatchilah. If we know that someone does not learn, we do not use him for testimony l'Chatchilah unless we know that he keeps Mitzvos and has Derech Eretz. B'Di'eved, we do not disqualify his testimony.

Rebuttal (Gra 37): He must have Derech Eretz, which includes the other matters.

Aruch ha'Shulchan (18): Derech Eretz is a job. One who makes no contribution to society (through Torah or work) may not testify.

Shulchan Aruch (18): Mid'Rabanan, disgraceful people are Pasul for testimony. These are people who eat in the market in front of everyone, walk naked in the market when doing disgusting work, and similar things that show that they have no shame. All of these people are like dogs; they are not concerned about false testimony. This includes people who publicly take Tzedakah from Nochrim even though they could do so covertly.

Beis Yosef (DH ha'Ochel and DH veha'Rambam): The Tur explains according to R. Tam that the disgrace of eating in the market is that he fixes his meal there. Meisharim says that the Rambam holds like R. Tam. I see no source for this. It seems that the Rambam holds that the Pesul is only if he eats in front of many people.

SMA (45): One who has no shame could testify falsely without concern for the shame if it will become known.