Kroxy seems to reset his inventory whenever he goes walking. Wait outside of his shop until he walks off. Then, when he reappears inside of it (I don't know how he does it, either, maybe Kroxy has teleporter pyramids, too), his stuff should be refreshed. I used Divine Death/Resurrect on the wimpy Imp Chieftains for phat lewt, then loitered around Kroxy's shop until he went for a stroll.
He won't leave if you're in his shop, of course, so wait outside near the wagon. Few other shop keepers reset their inventory in any reasonable amount of time, that's why I so love Kroxy.