that if you factor in the service cost to the asking price and are transparent should be up to the buyer. I know though it can be a real drag...I recently purchase a Zenith Chronograph that was supposedly serviced and working fine.....it too was about 17-21 secs off daily....the cost of the service
try "Blue Magic" Metal polish cream.....works wonders on plexi and is really safe as concerns wearing the plastic too thin. Always use only hand motion and pressure......been using if for years to correct small lines and other issues in all types of plastic.