Amazon.com: International Shipping
The above link says so. It means, if you purchase from amazon global saver,they calculate the import duties for you and collect in initial stage. If customs do not charge duties for your product, amazon will credit the amount back once they get the update.
So, if you do not purchase product with amazon global saver, they may not collect the duties initially which you have to pay once it arrives (few were lucky to get passed thru customs without paying much). Some were unlucky and they had to pay 20-100% duties at times :)
Hope you got a better idea . Or did i confuse you further?