Related for Gittin 60:9

[If the owner of a field] said to him, "Go out and gather figs for yourself from the fig tree," he may eat casually from them and tithe them as certainly untithed produce. [If he] said to him, "Go out and fill yourself up this basket," he may eat from them casually and tithe them as Demai. In what case does this apply? With [a field belonging to] an am ha'aretz, but with [the field of] a chaver, he may eat and there is no need to tithe, the words of Rebbi. Rabban Shimon ben Gamaliel says, In what case does this apply? With [the field of] an am ha'aretz, but with [the field of] a chaver, he should not eat until he has tithed, since chaverim are not be suspected of taking Terumah [on behalf of other produce] that is not in close by (and thus we can be certain that the chaver-owner would not have already tithed these figs (see Ter. 4:3)). Said Rebbi (not "Rabbi Yehuda"), my words are preferable to the words of Rabban Shimon ben Gamaliel. It is better that chaverim will take Terumah [from produce] that is not close by and not feed untithed produce to amei ha'aretz.

Rabbi Yehudah says, [with respect to] a place (i.e., a vineyard) that typically produces Olelet (defective clusters), a poor person [selling wine in a location near the vineyard] is believed to say, "This wine is from Olelet" and that he gathered it as part of his gathering. [If he said,] "I and my brother," or "I and my close relative [gathered these grapes]" [he is also believed], but he is not believed to say "From such-and-such Gentile I bought it," [or] "From such-and-such a Samaritan man I bought it." The poor among the Samaritans are like the poor among the Jews [in this respect], but the poor among the Gentiles are not believed in any matter.