First-class and second-class products mainly depend on whether there are impurities in the design and color, and whether it is flat when viewed horizontally. The third thing is to look at the base. In fact, many merchants sometimes distinguish between first-class and second-class products. If the products are sold as a mixed bag, you can still see the clues in comparison. The quality of first-class products and second-class products from some manufacturers is almost the same, but there seems to be a difference in color.