Shortly i'm going to be going to China, and everyone knows that China (namely the large cities--hong kong, shanghai, and beijing) is a great place to pick up electronics cheap. But its also a great place to get screwed.

Anyone have any advice on how to make sure you dont get a defective piece of crap. Obviously i dont mean chain stores--i.e. bestbuy. I'm mainly curious about Shanghai, and i've read that there are many massive markets for electronics which carry name and off name brands. are those name brands the same as they are in the US?

Summary:
1) How do i make sure the item isnt defective?--any particular place in Shanghai which is known for being reputable.
2) Any electronics i should just stay FAR away from?
3) Also advices on bargaining?--What is their bottom dollar (on average). (50% of the price they're asking? less? more?)
4) What i'm mainly looking for: SSD, HDD (int/ext), Camera Lenses/Equipment, Computer hardware/accessories.