1) Rashi on the Mishnah says that once the ba'al is mafrish the terumah, he should sell it to a kohen and keep the money for himself. However, if the terumah was already transferred to the kohen through either makarei kehunah or zechiyah, why should the produce still be assur for the ba'al to eat?
2) According to Rashi's understanding of Rav, granted that the terumah becomes mamon ha'shevet, at what point in time is the mitzvah of nesinah being fulfilled?
Anonymous, Woodmere
1) Terumah possesses Kedushah, and this holiness can never be taken away from it. Therefore, the Ba'al is not required actually to give the Terumah to the Kohen, since by foregoing the loan that the Kohen owes him he now has no monetary duty to give Terumah to the Kohen. The food, though, remains holy, so it must be sold to a different Kohen, since only Kohanim are allowed to eat Terumah.
2) The Mitzvah of Nesinah is fulfilled as soon as the produce becomes liable for Terumah, i.e. as soon as there is "G'mar Melachah," that has finished being worked with. For example, once he smooths out the pile of wheat, the obligation to give the Terumah to a Kohen automatically takes effect, and since it is obvious that he will give the Terumah to his regular Kohen, it is as if he has already given it and thereby fulfilled the Mitzvah of Nesinah.
Kesivah v'Chasimah Tovah,
Dovid Bloom