(Mishnah): If one sells his slave to a Nochri or to Chutz La'aretz, the slave becomes free.

We do not redeem captives for more than their value. This is a decree for Tikun ha'Olam.

We do not help captives escape, for Tikun ha'Olam;

R. Shimon ben Gamliel says, this is to help captives.

We do not buy Sefarim, Tefilin or Mezuzos from Nochrim for more than their value, due to Tikun ha'Olam.

(Gemara): [We fine one who sells his slave] to a Nochri even in Eretz Yisrael, and [one sells] to Chutz La'aretz, even to a Yisrael

Question: Who frees him?

Answer: The first master gives his value [for it was a Mekach Ta'os, i.e. a mistake sale], and the second frees him (for according to letter of the law, it is his slave).

Question: We should say that if the second master knew [that he is a Yisrael's slave from Eretz Yisrael, it is not a Mekach Ta'os], and both of them give his value (i.e. the buyer gets back only half), and if not (the buyer did not know), the first master gives his value, and the second frees him!

[If one wrote] 'I, Ploni ben Ploni sell my slave to Ploni of Antuchi (a place in Chutz la'Aretz)', he goes free. [If he wrote that the sale is] `for when he is in Lud' [even if the buyer later took him to Chutz la'Aretz], he does not go free.