@GlobalExport
First of all, I can see you're hungry and I respect that. When I first came to Hong Kong I actually did what you're hoping to do. Me and a pal went to Guangzhou (like Shenzhen but bigger and cheaper) and we bought tablets and bluetooth headsets, what else...SD cards...he also bought clothes for his wife's clothes shop...over the years we have done business in Shenzhen with paper, printing, books, some other electronic items and some other textiles...anyway, I'm not an expert, but I do have experience with these guys. Further, I live in Hong Kong and my wife is Chinese, can speak Putonghua.
I'm going to tell you what it is like in China...
1.) They are all going to scam you. You can speak to a guy a T-shirt shop and he will tell you he has a factory that makes phones...everyone will tell you they have a factory. If you look on Alibaba for long enough, you'll be surprised at how many of these traders 'own' the same silver and glass clad factories and they are always managed by pretty 20 something year old girls, according to the pictures. Alibaba is a club, you pay for higher levels of membership...Finding the 'source' is a freaking magic trick mate, I'm telling you, you will not be doing that on your first trip to S.E.G. Please fucking forget about that right away.
2.) Even if you find the source my friend. Can you imagine the M.O.Q.s these factories deal in? They are not going to deal with you. I once hit the holy grail and found myself in a real genuine factory in Shenzhen...after months of false leads!! Well, yes, they want to do business with me okay...M.O.Q. 3000, that on a n item I only wanted 50 of!! They said they were offering that to me as a one off, normal M.O.Q. is 15000 pieces. These companies supply the world, not individuals.
3.) There are sourcing/trading companies all over HK who make their business sourcing for overseas companies, you're not smarter than Walmart.
4.) People do come to HK and do what you want to do...my understanding is that they tend to buy the phones at Chungking Mansions...that's in Hong Kong...because it's cheaper here!
5.) What can go wrong? Mate, you can't even imagine how amazing these guys are...you'll start selling your Chinese sourced phones and, oh oh, it said 32gig....hey, it's only 8??? You said 8mp camera, this is only 1.3, etc, etc, etc....yeah, we had it, 8gig SD cards, beautifully packaged, hey presto, only 2 gig inside...these guys work on such wafer thin margins that they will destroy you to squeeze such small amounts of RMB from you that it will make your eyes water.
Anyway, good luck.