Maaser Sheni, Chapter Three, Mishnah One
We learned in the first mishnah of the tractate that it is forbidden to sell maaser sheni. Our mishnah teaches that it is also forbidden to make certain deals that make it look as if one is selling maaser sheni.
1) One should not say to his friend: Carry up this [second tithe] produce to Jerusalem that in order to divide it.
2) Rather he should say to him, Carry it up that so that we may eat and drink of it in Jerusalem.
3) But people may give it to one another as a free gift.
Section one: The problem with this type of arrangement is that it looks as if he is using maaser sheni produce to pay his friend to help him carry it to Jerusalem. Therefore, this type of statement is prohibited.
Section two: If he doesnt use the word divide then this is permitted. All he is doing here is asking his friend to help him carry the load to Jerusalem so that they can eat and drink it together there.
Section three: If someone wants to have another person carry his maaser sheni for him to Jerusalem, he is allowed to give it to him as a gift. When they get to Jerusalem, the one who carried it can give some of the maaser sheni back to its original owner. Of course, he takes a risk in doing somaybe his friend wont give it back to him! But if he doesnt, then he wasnt really much of a friend to begin with.
This same halakhah was also taught in the first mishnah of the tractate, but there it was not taught in connection to this specific issue.