(R. Yirmiyah): Who is the Tana that prohibits selling Ma'aser Sheni? R. Meir, but R. Yehuda would say that it should be permitted, based on a (different) Kal Vechomer...If Sheviis, with which one may not pay off a debt, is permitted to sell; Ma'aser Sheni, with which one may pay off a debt, should certainly be permitted to sell.

Where do we find that one may use Ma'aser Sheni to pay off a debt? As the Mishnah taught (later Perek 4, Mishnah 4 - see Bechoros 57) - if the buyer drew Ma'aser Sheni (from the seller) worth a Sela and before he had managed to redeem it, it became valued at two Sela (he gives him a Sela and gains a Sela and the Ma'aser Sheni is his. If the buyer drew Ma'aser Sheni worth two Sela and before he managed to redeem it, it stood at the price of one Sela, he gives him one Sela of regular money and he may give a Sela of Maaser money. In that case, the buyer has a debt of two Sela to the seller and he uses Ma'aser Sheni money to pay it off.)

Rebuttal (R. Yosi): That case is different, as from the first moment, he was obligated in a payment of Ma'aser Sheni. It would only be a proof if he was obligated in a regular debt and he would be permitted to pay Ma'aser Sheni money.

(R. Yudan): We find a Mishnah that forbids him to sell it - (Maseches Kidushin 2:8) - '(If a person betrothed a woman with Ma'aser Sheni money, with inadvertently or intentionally, she is not betrothed. R. Yehuda says that) if intentionally, it is a valid betrothal; if done inadvertently, it is not valid.' If you say that it is permitted to sell, it is permitted to betroth with it. If not, it is prohibited.

And anything that's prohibited to sell is also prohibited to use to betroth, as the Mishnah taught (in Maseches Sheviis 8:8), 'One may not buy slaves, fields and impure animals with Sheviis money and if he did, he is penalized that he must consume the equivalent amount of other produce as Sheviis produce.

(R. Yosi): This shows that it's forbidden to betroth a woman with Sheviis money, as it's no different to acquiring a maidservant using Sheviis money.

(R. Yosi citing R. Zeira/ R. Yudan citing R. Yaila): Our Mishnah follows all opinions (as even R. Yehuda agrees that one may not sell Ma'aser Sheni), because it disgraces it.

(R. Yosi citing R. Acha): All agree that one may not sell it, so that all will come to Yerushalayim to consume it (thereby bringing them to fear of Heaven).

The Mishnah taught that one may not use Ma'aser Sheni as collateral. How is this? If a creditor enters the debtor's home to take collateral on the loan, the debtor should not give him Ma'aser Sheni.

(Baraisa): It should not be given as a guarantee for a new loan, nor should it be given to a shopkeeper so that he will sell him food.