(Beraisa #1): If one gave coins to his friend to buy for him wheat, and he bought barley, if [the seller] gave to him too little, [the Shali'ach] suffers the loss. If he gave to him extra, he [the Shali'ach] gets the extra.

(Beraisa #2): If he gave to him too little, he [the Shali'ach] suffers the loss. If he gave to him extra, the extra is [shared among] both of them.

Question: What is the reason of R. Yehudah (the author of Beraisa #1 - Demai 6:8)?

Answer: The seller intended only for the buyer (the one who gave to him the money) to acquire.

Objection: Why does he not divide with him? (The profit came also through the Meshale'ach's money!)

Answer: One may not benefit from another. (The seller intended only for the buyer.)

Question: If so, we should say [that the buyer keeps the extra] even if he told him to buy for him wheat, and he bought for him wheat!

Answer: [Then,] the seller intended only for the owner of the coins to acquire. When he told him to buy wheat, and he bought barley, the seller intended only for the buyer to acquire.

Objection: Does [the seller] know (whether or not the Shali'ach deviated)?!

Answer #3 (R. Nasa): (The seller always intends for the buyer in front of him.) When he fulfilled his Shelichus, the seller did not intend for the owner of the coins to acquire. (Rather, the owner acquires, for his Shali'ach is in place of him.) When he did not fulfill his Shelichus, [the seller] intended for the buyer (i.e. Shali'ach, who buys for himself) to acquire.

Question: [In Beraisa #2] why does he divide with him? (The author, R. Yosi, holds that the seller intends for the owner of the coins!)

Answer: Since [the seller] benefited through him (the Shali'ach chose to buy from him, he wants that the Shali'ach) divide [the extra] with him.