When Zach and I were in the Pearl River Delta for The Public Radio in late July, we took a few trips to the infamous Shenzhen electronics malls. A few notes:

This is an ecosystem. Calling them "malls" kind of misses the point. Western style malls are just the end of the supply chain; the Shenzhen electronics malls are almost a full supply chain unto themselves.
I don't know how many independent businesses actually work in these places, but it seems like it must be in the high four figures at least. Many of them (especially on the lower floors) don't seem to be any bigger than a chair and a tiny countertop; others are weird outposts owned (apparently) by major international brands.
Everywhere in the malls, work is being done. I can't stress this enough - people are doing real, tangible work. This is perhaps the most striking part about them, and it contrasts directly with what we're used to in the US (where teenagers at Abercrombies mostly sit around, stock shelves, and run credit cards). You don't even have to look that hard - at the mobile phone mall on the south side of Shennan Middle Road, there are people at almost every shop who are literally putting phones together in plain view. Similarly, at Huaqiangbei you can see people (for instance) making wire assemblies at their tiny counters. The fact that you're buying services is totally apparent here.
*Nobody* was phased by our presence. There were very few white people in sight (especially on the upper floors, and at more obscure malls), but (aside from small children) nobody really cared that we were there at all.

As a final note, a rather remarkable thing happened since we returned from China. My old MacBook Pro had a hardware failure, and the problem appeared to be the hard drive cable (apparently they tend to go bad on my particular model). I ordered a new one on Amazon, and when a week went by (I hadn't really looked at the shipping time estimate), I checked to see its status. Well it turns out that the cable was sent to me directly from Shenzhen. I have no way of knowing, but I wouldn't be surprised at all if it came from one of these malls.