Maaser Sheni, Chapter One, Mishnah One
The Torah calls maaser sheni holy (Leviticus 27:30). Our mishnah teaches that it must be treated as holy produce and not as one would treat hullin, non-sanctified food.
1) Second tithe: one may not sell it, use it as a pledge, exchange it, or use it as a weight.
2) One may not say to his friend [even] in Jerusalem: Here is [second tithe] wine, give me [in exchange] oil, and the same with all other produce.
3) But people may give it to one another as a free gift.
Section one: It is forbidden to act in any of these ways with maaser sheni because this is how one might typically treat non-sacred produceone sells it, uses it as a pledge to secure a loan, and one exchanges it with friends. Using it as a weight does not refer to actually weighing maaser sheni but rather it refers to using maaser sheni whose weight is known as a counterweight on a scale. The mishnah is probably referring to maaser sheni coins which were exchanged for the maaser sheni produce.
Section two: This section emphasizes that one cannot exchange maaser sheni products one for another, even if one is in Jerusalem, where maaser sheni must be brought. Again, this is not considered a respectful act and shouldnt be done with maaser sheni.
Section three: Giving maaser sheni to another person as a present, when one does not expect anything in return, is not disgraceful and therefore it may be done.