Related sobre Ketubot 2:18

[A seller who] said "this is mine (i.e., from my fields)," they are liable to tithe. [A seller who said] "it is tithed," they are believed because the mouth that forbade is the [same] mouth that permitted (cf. Dem. 6:11). [Someone who] sold produce in a year [when one is obligated in the laws] of second tithe, and said, "[This produce has been separated from] second tithe," they are believed. [Someone who] sold produce in a year [when one is obligated in the laws] of the poor man's tithe, and said, "[This produce was separated from tithes during a year of] second tithe," they are not believed. [Someone who] sold produce in a year of second tithe and said, "[This produce was separated from tithes during a year of] poor man's tithe," they are believed, because the mouth that forbade is the [same] mouth that permitted.

Witnesses that said, "We testify about Ploni that he is a son of a divorcée" or "son of a halutzah (woman who was eligible for levirate marriage but went through the halitzah ceremony instead)", "a natin (descendant of a Canaanite Temple servant)", or "a bastard (mamzer)", [but] before their testimony was investigated in court, they said "We are liars"—behold they are believed. If after their testimony was investigated in court they said "We are liars", they are not believed. This is the rule of the matter: Witnesses that testify to declare something impure, pure, to distance, to bring closer, to forbid, to permit, to exempt, to obligate—if, before their testimony was examined in court they said "We are liars", they are believed; [but] if after their testimony was investigated in court they said "We are liars", they are not believed.

And similarly with two men—this one says, "My fellow is a kohen" and the other one says, "My fellow is a kohen"—they give to them [the priestly gifts]; but for priestly pedigree [i.e. to pass onto their children] they are not believed until there are 3 men, in order that 2 of them testify about the 3rd and the other 2 testify about the other 3rd. Rabbi Yehudah says: They don't even give them [the priestly gifts] until there are 2 to testify about this one and 2 to testify about this one. They raise someone to the priesthood, to being a Levite or an Israelite on the basis of one witness; but they do not lower someone except on the basis of 2 witnesses. Rabbi Yehudah says: Just as they don't lower someone except on the basis of 2, they don't raise except on the basis of 2.

If rumour was spreading in town—Rabbi Yose says: Rumour is not evidence, rather anyone who has a valid legal complaint should come [to court] and say it. Rabban Shimon ben Gamliel says in the name of Rabbi Shimon ben Ha-Sgan: They raise [someone] to the priesthood based on 1 witness, and not even just 1 witness but even on the basis of a woman['s testimony]. And the woman doesn't even have to come to court, just when she said "They gave to him" [his priestly gifts, this off-hand comment is enough to raise someone to the priesthood].

A man is believed to say, "My father said to me that this family is impure"; "This family is pure"; "We ate in the ketzitzah of Plonit [see Lieberman: a ceremony for when one of the men married a woman who was not fitting for him]"; "Ploni's teacher said to him, 'Go and immerse your terumah!'"; or "We used to bring terumot and tithes to Ploni"—they are believed to give to him [his portion] but not as a grounds to presume he is a priest [for the purpose of passing on that status to his children]. But [if they testified] "Others used to bring to him [his portion]", they are not believed (although, Ehrfurt: they are believed). If [they testified] "He was a Gentile and converted", "A slave and he was freed"—then these are not believed. They are not believed to say, "I remember that Ploni owed Plonit (Ehrfurt: Ploni) a maneh"; or "Ploni's path went through Ploni's field" since this is like monetary cases. Rabbi Yohanan ben Berokah says: They are believed.

Said Rabbi Yohanan ben Berokah: A wife or minor is believed to say "From here the bee swarm left". When does this apply? When they are testifying right there. But if they go out and come back, they are not believed, since they only say this because of persuasion and fear [that people with power over them have instilled in them]. Men, wives, slaves and minors are believed to say "This place is impure" or "This place is pure".