An ignoramus is ineligible for a witness.
The following are ineligible as witnesses of the appearance of the new moon:—Dice-players, usurers, pigeon-fliers, sellers of the produce of the year of release, and slaves. This is the general rule; in any case in which women are inadmissible as witnesses, they also are inadmissible here.
Rosh Hashanah, fol. 22, col. 1.
Two disciples of the wise happened to be shipwrecked with Rabbi Yossi ben Simaii, and the Rabbi allowed their widows to re-marry on the testimony of women. Even the testimony of a hundred women is only equal to the evidence of one man (and that only in a case like the foregoing; it is inadmissible in any other matter).
Yevamoth, fol. 115, col. 1.
"Whosoever is not instructed in Scripture, in the Mishna, and in good manners," says Rabbi Yochanan, "is not qualified to act as a witness." "He who eats in the street," say the Rabbis, "is like a dog;" and some add that such a one is ineligible as a witness, and Rav Iddi bar Avin says the Halachah is as "some say."
Kiddushin, fol. 40, col. 2.
Even when a witness is paid, his testimony is not thereby invalidated.
Kiddushin, fol. 58, col. 2.