‘Behold, I will stir them up out of the place where you have sold them,
And will return your recompense on your own head,
And I will sell your sons and your daughters into the hand of the children of Judah,
And they will sell them to the men of Sheba,
To a nation far off,
For YHWH has spoken it.'
But YHWH would not leave His people in the places where they had been sold. One day He would stir them up out of their place and restore them to Himself. And He would also recompense Himself on those who had stolen from Him. He would do it by Himself selling their children to Judah who in turn would sell them in the east, to the Sabeans (the opposite direction to the Greeks). If carried out at all this specific judgment would have been carried out in later centuries and is not to be seen as something that will happen in the future. YHWH's judgments extend over a long period before they are finally summed up in the final judgment. But there is good reason for seeing this as simply an example of retribution not to be taken literally. (It is quite clear that YHWH Himself would certainly not ‘sell slaves' to anyone).
‘To a nation far off.' Just as the Judean slaves had been carried over the seas, so would the Tyrian and Philistine slaves be carried afar off, for the Sabeans would sell them on to many places in Africa. And all this would happen because YHWH had purposed it. It would result from the powerful word of YHWH which always accomplished its purpose (Isaiah 55:10-13).
There is in fact no record of this selling of slaves to the Sabeans, and it is very possible that this was simply intended to say graphically, ‘what you have sown you will reap', or in Old Testament terms, ‘an eye for an eye and a tooth for a tooth'. As already mentioned, it is quite clear that YHWH would not literally sell slaves to Judah. It was simply His way of reminding the nations of what He could do if he wished, and what the future would hold for them in general because of their opposition to Him. It was also a guarantee of the prosperous future of Judah.