Yes, there is well-knon market in Sham Shui Po selling used electronic products. There is risk while buying an second hand stuff, isn't it. If you know the camera well, I think it is find. I know some one pay for a used OLLEI film camera for 900 yuan or HKD I don't know. You can walk from Ap Liu St to Cheung Sha Wan and then Jade Market in Tong Chau Street. You may find what you want.