I recenly bought a 15 kopeks 1861 with smooth edge (it's still in mail, so no pictures at this point).
Because it was cheap, I bough it without actually seeing the edge.

Do it exist, error coin perhaps, or was it just the seller talking?

Or it could be someone who had too much time and sandpapered the edge off. Possible - I've seen a few examples. You gotta take a look at the edge carefully.

If the edge is manipulated somehow, I'll notice it, I think. I'll put some pictures to this website...