Clarification: What advice did he give him?, explains Rashi; since he would not have told him to perform an Isur.

Implied Question: In fact, when he told him to go and steal and sell himself as an Eved Ivri, the Gemara could have asked the same Kashys - 'Since when is one permitted to advise somebody to steal and to do an Aveirah'?

Answer #1: Only the Gemara's response is fine.

Answer #2: Moreover, had the Gemara asked that, it could have answered - that he advised him to sell himself ...

Source: Following the opinion of Rebbi Eliezer, who said earlier (on Daf 14b) that in both cases (whether Beis-Din sell him or he sells himself) his master may give him a Cana'ani maid-servant.

Question: But did our Mishnah not say 'Ten Yuchsin went up from Bavel - one of which was ''Levi'im'?

Answer: All the Levi'im who accompanied Ezra had their thumbs cut off, and were consequently unfit to sing Shirah on the Duchen.

Refuted Explanation: In that they did not eat Kodshim, Rashi explains.

Refutation: But this is not correct, seeing as, in any event, one needs to be concerned that one may elevate them from T'rumah to Kodshim, and from Kodshim to Yuchsin?

Authentic Explanation: What 'Ri'a Chezkosaihu' therefore means is that - they searched for their certificate of Yichus but were unable to find it.

Clarification: It is fine according to the opinion that 'Ein Ma'alin', what 'Gedolah Chazakah' means is that ...

Clarification (cont.): … that even though we ought to have decreed, since they may come to elevate them to Yuchsin – because he does not hold of ‘Ri’a Chezkasaihu’ - they nevertheless did not do so.

Clarification (cont.): But according to those who hold 'Ma'alin', who (also) holds of the S'vara of 'Ri'a Chezkosaihu', what does 'Gedolah Chazakah' mean? ...

Clarification (concl.): Since the reason that we do not decree is because 'Ri'a Chezkosaihu. Tosfos Yeshanim].