Actually, that comm does not look too bad, at least from what can be seen. Lathe turning is a radical step, and reduces the life of a starter by quite a lot. Turning is a last resort. If there are no deep grooves in the copper, I would not turn it. A quick buff with fine emery clothe will clean it up. DO NOT allow anyone without comm turning experience turn your comm. And, the slots in the comm MUST be cleaned out after turning/buffing. I do this with a ground down piece of hacksaw blade, carefully.
As a tech in a electric motor shop for 20 years, I cleaned up thousands of DC motor comms in my time. Actually lathe turning a comm was a final resort to get a usable comm.
2003 Rincon 650 w/mods
2003 Rancher 350 w/mods