(Mishnah): One who buys produce from one who is not trusted for Maaseros and he forgot to tithe them, he may ask the seller on Shabbos and eat according to his answer. But once Shabbos ends, he may not eat until he tithes.

If Terumas Maaser that was separated from Demai became mixed into the original pile (so that there is no way to be able to eat it now), R. Shimon Shazuri says that even during the week, he may ask the seller if it was tithed and can rely on him to eat it.

(Gemara) (Chevraya citing R. Yochanan): They permitted trusting the seller on Shabbos in honor of Shabbos.

Question: If so, since he isn't trusted, why even ask him?

Answer: (By asking him) it gives a pretext to allow it.

(R. Baybei citing R. Chanina): The fear of Shabbos is upon the seller and he will tell the truth.

Question: If he told the truth, why does the Mishnah teach that after Shabbos he must tithe to eat?

Answer: Because of the one person who does not have the fear of Shabbos on him, we cannot rely on his word after Shabbos.

Baraisa: If he asked him on a weekday, he may not eat it on Shabbos.

Question: According to the opinion that 'the fear of Shabbos is upon him', it is fine; according to the opinion that it is in honor of Shabbos, even if he asked him during the week, he should be able to eat them..?

Answer: Permission was only give if it was unintentionally left, as the Mishnah taught, "If he forgot to tithe them".

He may only eat from the fruits if he did not stipulate (before Shabbos that if he forgets to tithe, they should be tithed from then); but if he did, he can eat based on the stipulation.

Question: Could a person eat based on another's question?

What's the case? If two people bought from the seller at the same time and one of them asked about the nature of the produce, the second person cannot eat until he tithes or himself asks the seller - as I say that perhaps the seller tithed this one's but not that one's.

If one person bought two baskets at the same time and he asked about one, he may not eat from the other until he tithes or asks about it - as I say that he tithed the first basket but not the second one.

The Mishnah taught: But once Shabbos ends, he may not eat until he tithes one for the other.

Question: According the one who said it's in honor of Shabbos, it is fine (as he was never believed that it was already tithed); but according to the one who said that the fear of Shabbos is upon him (and he truthfully said that the first basket was tithed), how could he tithe one for the other (since he is separating from that which is exempt for that which is obligated)? (The Gemara leaves this question unanswered.)

The Mishnah only permitted him to eat based on the seller's words when he doesn't have other tithed produce of the same sort, but if he does, despite this, since a person desires to eat what is forbidden to him, in honor of Shabbos, he is permitted to eat it.