Our company relies on sourcing products from China very heavily and we generally import by the container load (of course we started off with ~$1000ish shipments!).
I have a personal blog (zero advertising, just to help out fellow entrepreneurs) here: [chineseimporting.com
...] with a lot of, IMO, valuable information.
The biggest question is what are you importing? The more niche a product is, the less large the discounts will be. The suppliers will assume you know your product inside out. The more mass appeal your product, the more the suppliers will know there's a million entrepreneurs with small businesses who are looking to make a quick buck, and hence, the more opportunity for naive buyers :) Also, you have a muchhhh greater risk of encountering fraudulent suppliers.
The second thing is to remember, if you're not discussing importing by the container load, you have absolutely no leverage. You can get the market rate (Chinese price of course), but nothing lower. To determine the market rate you really have to get a few quotes. It's the most tried and true tactic in negotiation "Person A offered me the product for this price. Can you do better?". Don't lie. The factories will know if you are.
Third, price in China shouldn't be the biggest consideration. The prices in China will be ridiculously lower than North America and as long as you get quotes from a few companies, you won't get ripped off hugely. Quality of course is the most important thing. If you start demanding a very low price, you might get it but they will give you a much lower quality product without telling you (this isn't necessarily a scam- they expect you to know the fair price for a product and if you offer lower they expect you to know you must be getting a lower quality product). Other things to consider are how will the product be packaged? When will you get the shipment? Who will pay for freight? Etc etc.