Commentary for Avodah Zarah 115:11

For a reason not entirely clear, Rava does not want R. Huna b. Nahman to enter into his room. But he enters anyway. R. Huna b. Nahman asks Rava how he rules in a case where the non-Jew shook the wine but did not do so with the intention of libating. Rava, against what he said earlier, claims that it is forbidden for usage. R. Huna responds that Rava himself said that such shaking does not make the wine yayin nesekh. Rava responds that he agrees that the wine that was actually shaken is yayin nesekh. But since the storekeeper threw the wine into a barrel with unshaken wine, he need not lose the value of the entire barrel. He may sell the barrel but just reduce the value of the wine thrown in.
The Tosafot have another reading of this section. They read that it is not R. Huna son of R. Nahman who comes to Mehoza but R. Nahman, Rava’s teacher. This helps explain why Rava is afraid of him—he fears that he is contradicting his teacher. Rava now asks R. Nahman for the ruling, and R. Nahman responds that it is forbidden to even use such wine. Rava then responds by claiming that R. Nahman said that such shaking does not make yayin nesekh. R. Nahman concludes by saying that the value of the wine actually shaken is prohibited.
This is a much easier reading of the Talmud but it is not the text that we have in front of us, which follows Rashi’s reading.

Rava comes to Pumbedita, where Nahmani, another name for Abaye, is the head of the academy. Abaye proves to Rava that this wine is prohibited. First he cites some precedents, cases where rabbis actually ruled that it is prohibited.
Shmuel prohibited it in Nehardea. R. Yohanan prohibited it in Tiberias. Thus two great rabbis already ruled strictly.
Rava tries to argue that in these places they prohibited it because the people there are not “students of Torah.” Since they are not knowledgeable in the finer points of Torah, the law must be more stringent with them so that they will not come to transgress Torah law. But Abaye pushes back—if the people in Nehardea and Tiberias are not students of Torah, then all the more so the people in Mehoza, Rava’s place of residence, are not. Thus there is no justification for Rava to rule leniently.

The market inspector was not drinking wine for his own benefit. He was testing it to see what it was, perhaps its quality. Nevertheless, the rabbis prohibited not only the wine that he actually touched, but the entire cask that he threw the wine back into. This is a proof against Rava.

Rava tries to answer that it is prohibited only to drink the wine, but not to sell it. The problem is that the second half of this baraita uses the word “it may be sold” to rule that while it is prohibited to drink the wine, it is not prohibited to sell the wine. Thus, when the first half states “it is prohibited” the implication is that is prohibited to even sell the wine.
As far as the difference between the first half of the baraita and the second half, the rule seems to be that if the non-Jew knew it was wine, we must be concerned that he libated it, even if this is very unlikely. But if he thought it was oil, then we can be sure that he did not libate it, and thus the wine can be sold. Note that the rule is still strict with regard to drinking the wine. Even though the non-Jew touched it not even knowing if its wine, it is still prohibited.

The story is fascinating—we can see that the rabbis didn’t always know who was Jewish and who was not. After having poured the wine, the rabbis debate whether Jews may drink the wine, meaning it is totally permissible, or whether they may not even sell it, meaning it is totally forbidden.