Ok, folks, enough fooling around. We can go back and forth for ages on this.
On a spinner you should really use water. You really don't want to be breathing particles of plastic and resin. It's really dangerous.
By hand, you can do a few hand strokes to rough up the surface with anything: Scotch Brite pads, Abralon, Siaair velvet, sandpaper. But you don't want to sanding a ball from 4000 grit down to 1000 grit, or similar serious surface changes, by hand. It's just not going to be right. It may not be out of round (plastic, urethane and resin balls are pretty hard, in general) but sure is not going to be even or smooth. If you want it right, do it right.
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"None are so blind as those who will not see."