One thing that I do is remove the exhaust, and look up into the exhaust port of the cylinder. With the piston at bottom dead center (BDC), you can see the intake side of the cylinder wall, and look for scratches, discolorations, etc. Then, with the piston at top-dead-center (TDC), you can see the piston skirt surface of the exhaust side of the piston. While rotating the flywheel and moving the piston, you can also inspect the piston rings at their hottest point, and inspect for scratches and/or discoloration of the piston below the rings. You will also be able to note how much carbon is built-up in the exhaust port.
Hope this helps.