Related על כתובות 2:5

[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.