(Baraisa supporting R. Yochanan): R. Nechemia said - whether the Jew bought from a gentile merchant, or from a Jew, or from a Kusi, or from an Am HaAretz - it is Demai.

Question (R. Chiya bar Ada to R. Mana): Why not ask the merchant from whom he bought the produce - if from a Jew, it is Demai and if from a gentile, it is definite Tevel?

Answer: The merchant was a gentile and a gentile and a Jew both brought him produce and he did not from whom he bought it; it is Demai.

Question (Rav Hoshiya): But there is a Baraisa that supports R. Yochanan - R. Yehuda said - the Chachamim only referred to Badan pomegranates and Geva grass when discussing the law that they are tithed as definite Tevel everywhere (as only gentiles grow them). What is the case? If a person bought them from a Jewish merchant, could we say that it is definite? (Perhaps the merchant tithed it!) Rather, he buys it from a gentile. However, for other produce, even when buying from a merchant, it is Demai. (This supports R. Yochanan!)

(R. Shmuel bar Rav Yitzchak): It is actually referring to buying it from a Jew, (but it is definite Tevel rather than Demai) because he is a large-scale middleman and the government officials are pressuring him to sell at a low price. The Chachamim allowed him sell produce without first tithing, leaving the buyer to take care of the tithing himself.