Are you sure the porcelain is scratched? Scrubbing with BonAmi, Comet, etal, can get rid of surface marks left by metal.
If it is actually scratched, have you contacted him, or his company, to notify him/them of your complaint?

Thanks for your response, randy427. After I posted this message, I found another source that suggested using Barkeepers' Friend. Interesting -- when I used the BK and cleaned with the toilet scrubber, the marks did not come out. When I poured a half-cup of the BK liquid into the bowl and let it sit there for 30 minutes, the marks were gone.