“For the seller will not return to what is sold, though their life be yet among the living, for the vision is concerning the whole multitude of them. None will return (turn back). Nor will any strengthen himself in the iniquity of his life.”
There is a play on words here. The word for multitude has previously meant the multitude of wealth, here it probably refers to the multitude of people. The seller will not return to goods that he can sell in the markets of Jerusalem, even if he survives, for the vision refers to the whole multitude of people, they will either be destroyed or removed far away. None of them will be able to turn back. Not one of them will return.
‘Nor will any strengthen himself in the iniquity of his life.' This may refer to false trading (compare Amos 2:6-7). They will no longer be able to engage in false trading and so enrich themselves and strengthen their position. It would equally apply to all men's sinful pleasures which boosted them up and made them feel good. All that will inevitably be over.