Is it definitely low on compression? Have you done a compression test or anything? I used to do this all the time with old lawn mowers and things. I do work on small engines as a hobby. Why would you want to polish the piston? Is it scored or anything? If it's low on compression, it would be a ring issue, not a piston. As long as it is physically, not scored or damamed then you could probably get away with rings.
Have you taken it aparts? If you haven't, I have had much success in taking them apart, and freeing the rings, as there are often seized after sitting for a long time. Then I make sure everything is really clean, and free of gum, and sludge. It usually works fine. Mine want to hone the cylinders a bit, as well.
Also, for a small engine, I have actually "deglazed" the cylinder with some extra fine wet sand paper and oil, and making a cross hatch pattern. Just don't work in one spot too long, and it's not a problem. It helps the rings "reseat" nicely. (I know this is a "no no" but it's not a race car, just a small engine) I have had quite a few lawn mowers (and actually a couple dirtbikes as well) work perfectly fine for years with this. I am still using my main dirtbike, and have been for years. It was seized when I got it, and I did this (along with some other things, of course) and it's been working for about 6 or 7 years now, racing and all.
Just my advice