Many local vendors here in China stock basic things, but if I want anything higher performance, they will order it for me and it is a little cheaper than Newegg, but a little higher than taobao. The things you want to stock are accessories, like I mentioned above. It is very difficult to compete online and worldwide since many people on ebay, taobao, alibaba and more will have more purchasing power than you and can undersell you. But if you make a local shop first, and become friends with a few people in the online circles, then you could make a good local business.
Stock all the small things, a few CPUs a few common video cards, a few common cases, then order everything else from good online sources that are close to you with fast shipping. So you can supply your local customers with anything they need at cheaper than local prices. Some of our local vendors sell everything, even high end parts... but since they always keep a high stock, their prices are sky high and people only go there for emergency buys.
But I have worked the retailing from different sides. My first job when I was 16 was for Wal Mart in the electronics section. They will sell things like computers and TVs below cost just to get people in the store to buy other things. For example, if you want to purchase a large TV, Wal Mart might only make $5-20. If you buy a 3 foot (1 metre) coaxial cable wire for $5... They just made $4.50.
Then I used to work for a Printer manufacturer that makes handheld barcode scanners that can print too (Monarch Paxar) and when they sell a printer they don't make much money... when you send it in for repair, we would charge you $100 for a $0.02 part.
So again, the moral of the story is start small and make sure you keep lots of small accessories, because the small things will make you rich slowly, but the high ticket items can make you poor quickly.