How is it possible that shipping of eBay items from China to US is 'free'?
The major reasons that I understand are that:


the Chinese government subsidizes shipping.
the US Postal Service, eBay China, and Hong Kong Post office have a trilateral agreement called the ePacket service which roughly speaking, allows shipping of small packages to the US at bulk pricing (instead of at the price for individual sales).


I don't think it's common for there to be "free" shipping though.

I'm retracting the part about China subsidizing exporters.