Precious metal products have imprints representing the fineness of precious metals, for example, pure gold 999 represents gold with a content of 99.9 percent, Au750 represents 18K gold with a content of 75%.. Consumers should pay attention to whether the product's imprint is consistent with the salesperson's introduction when purchasing. If there is any doubt about the quality of the product, it can be sent to the Gold and Jewelry Testing Center of the Quality Inspection Institute for testing by instruments.