That piston is significantly damaged - it looks as if someone has run it without oil in the petrol. There seem to be score marks running across the piston rings as well, but it's hard to tell from the photo. The score in the cylinder is probably more important though - piston scoring is most important when it reaches all the way to the skirt and the induction process is port controlled. If there is any scoring or roughness on the outside surface of the piston rings, that is a critical fault and they must be replaced.
It would be possible to remove the rings, polish the piston exterior with very fine wet-and-dry or something similar, fit new rings, and give it a try. How well it worked out would depend mostly on that cylinder score you mentioned. That will bypass the rings causing blow-by, and the blow-by will erode the new rings and ruin them much sooner than wear would have. So, how much do you intend to use this trimmer? If it just sits in the shed and you occasionally cut the edges at home, it may last several years. If you are a contractor, forget it.
