To my knowledge it is not unethical nor illegal for a jewelry appraiser to perform services on poor quality items as long as the items were correctly identified and graded fairly. I dont think appraisers discriminate against poor quality jewelry. They get paid to do a job just like everybody else. Buy better quality nexttime.
I dont think anybody should be buying jewelry for investment unless they really know what they are doing and have solid resources. Leave that for the experts in the trade.