(Chevraya citing R. Yochanan): (The Mishnah taught that a shopkeeper may not sell Demai) This is to prevent the children (who buy there) from eating Tevel.

Reason #2 (R. Ila citing R. Yochanan): When selling a small quantity, since the seller makes a large profit, the seller must tithe; when selling a large quantity, where the profit margin is small, which is a benefit to the buyer, the buyer must tithe.

There is a Baraisa that supports each of them. The Baraisa that supports the Chevraya - R. Nechemia said - if he sells in small quantities and the buyer wishes to add a Se'ah to the purchase, he becomes a seller of large quantities and the buyer separates. If the opposite happened, he becomes a seller of small quantities and the seller separates.

The Baraisa that supports R. Ila - R. Yishmael son of R. Yochanan ben Beroka said - if he measured for him with a small measure, the seller is obligated. Even if he only measured out 11/4 Seah, he must tithe the extra 1/4.

(R. Zeira): Sometimes a calculation must be made as to who gains more (whether the buyer or the seller) and he should therefore tithe. For example, if the buyer asked for several Reviyin (quarters of a Se'ah), fixing a price for each Rova. If the seller then combined all of the Reviyin into Se'in and sold them to him as Se'in and the fractions as Reviyin, since the seller gained from the deal by selling them as Reviyin, he separates. If they did the opposite, since the buyer gained, he separates.

(Mishnah) (R. Meir): If something that is usually measured out in small quantities was measured in a large quantity, it is treated as a large quantity (and the seller is exempt from Maaser Sheni). If something that is usually measured out in large quantities was measured in a small quantity, it is treated as a small quantity (and the seller is obligated in Maaser Sheni).

What is a large quantity? For dry produce it is three Kav and for liquids it is a Dinar.

(R. Yosi): Fig baskets, grape baskets and boxes of vegetables - as long as he sells them through estimation (rather than size), they are exempt (as they are treated as if sold in large quantities).

(Gemara): According to this Tanna, they gave a quantity for dry produce but not for liquid. They gave a value for liquid, but not for dry produce.

Baraisa (R. Chiya): A large quantity for liquids is a Hin; less than that is a small quantity. The value of a Taman (a type of coin) of dry produce is considered a small quantity; more than a Taman is a large quantity.

According to this Baraisa, they gave a quantity for liquid but not for dry; they gave a value for dry but not for liquid.

(R. Yochanan citing R. Shimon ben Yehutzedek): It is a stipulation of Beis Din that Terumas Maaser should be given by the seller and Maaser Sheni by the buyer.

What is the case? If the seller sells in small quantities, since the seller benefits, he separates; if he sells in large quantities, since the buyer gains, he should separate...?

Answer (R. Bun bar Chiya): The stipulation applied when the seller informed the buyer that he was selling his own produce.

(R. Yosi): Even if it's not his own produce; the case is when one suggested to the other that they should fix up the produce, but nevertheless, they must follow the stipulation of Beis Din.

(R. Elazar citing R. Hoshiya): It is a stipulation of Beis Din that when a butcher sells meat, he must cover the expense of removing the Chelev (forbidden fat) and the expense of removing the Gid HaNasheh (sciatic nerve) must be covered by the buyer.

R. Abahu set up in Kisarin that both expenses should be covered by the buyer, so that the butchers would remove them properly.