I've only been in Shanghai a few weeks but a friend introduced me to Kitty at the the pearl market in Yu Gardens.
Kitty is very sweet and gives a good price without much barter.
I know Nerdia said Yu Gardens was not so good but it's the only place I know so far. All I have bought are very inexpensive
and fun items (see my album for examples) and I don't know anything about pearls yet but if you have time after visiting
Hongqiao and want to visit Yu Gardens here is the info:
--Gina