Jamieson, Fausset and Brown on Joel 3:8

8. sell them to ... Sabeans--The Persian Artaxerxes Mnemon and Darius Ochus, and chiefly the Greek Alexander, reduced the Phoenician and Philistine powers. Thirty thousand Tyrians after the capture of Tyre by the last conqueror, and multitudes of Philistines on the taking of Gaza, were sold as slaves. The Jews are here said to do that which the God of Judah does in vindication of their wrong, namely, sell the Phoenicians who sold them, to a people "far off," as was Greece, whither the Jews had been sold. The Sabeans at the most remote extremity of Arabia Felix are referred to (compare Jr 6:20; Mt 12:42).