The young son of the Chinese owner of the violin is near-sighted and his glasses have concave lenses. When he attends the auction as an adult he is far-sighted with incredibly thick convex lenses.
When the servant is reading the Italian woman's cards, look at the justice card. It pictures a person in front of a red flag with a yellow star, a lot like the Chinese flag. In the next scene, (after the children's performance), the Chinese woman is standing at her podium in front of a Chinese flag; red with yellow stars.