Related к Бехорот 4:14

One who sends fruits to his friend, and he [presumably the friend] decides to return it, he comports himself [vis-a-vis the returned fruit] according to how it was (i.e., its prior status). Abba Shaul says, "I would be concerned lest it be switched." Rabbi Shimon ben Gamaliel says, "If he has a sharecropper who knows how to tithe, but he (i.e., the landowner) does not trust him as to tithes, and he (i.e., the sharecropper) brought his fruits to him, and he said, yours (i.e., your share) are tithed, he is believed [in this instance]." Rebbi says, "He is not trustworthy [according to the principle] that one who is suspected regarding [one] matter may neither adjudicate nor testify" (Bekh. 30a:3).

An am ha'aretz who said, "This is untithed and this is Terumah," [or] "This is certainly untithed and this is Demai," even though they said that a suspect in a case can neither judge nor testify in [that case], we do not suspect a [fellow] Jew on such a thing [and he may be believed].