For you have enough time in Shanghai, I suggest you go to Zhuji, the pearl city to look for pearls. There are some pearls stores around Yuyuan Garden area. If you do not have local friends to be your guide there, you had better to know some skills to know natual or manmade ones. In some brand pearls stores, it is safe for they can guarantee the quality of the natural pearls. If you are interested, you can have a short visit to the pearl markets in Zhuji, nearly three hours trip from Shanghai.