Using DHgate to purchase from China

If I make, say a jewelry purchase from a vendor in China for under $1000, and am offered free shipping through EMS, what can I expect in customs charges if any?

You may be lucky and your purchase will slip through. Then again, you may not. Where are you located? You can check the Customs tariff in your country to get an idea of what you might be charged. If you are in Australia then you should be fine, because purchases under $1,000 aren't charged duties (last time I checked).