Friend of mine works for a company that does all the fee calculations for FedEx shipping international. It is a very complicated formula because it is based upon a number of variables and it changes from year to year as every country publishes their book once a year as trade agreements change, etc. (Although she is primarily working with air freight, she got her broker's license a couple of years ago which is one of the more difficult licenses to obtain: only something like 20% pass on the first try, but with it she could work for the ports if she decided she wanted to leave her current position.) As I understand it, each country publishes their tarrifs every year and it is all broken down by item. This is the cost for pencils, this is the cost for napkins. This is the cost to ship napkins from point A to point B vs. point C. The ports have a fee system in place that are specific to each port. Fees for being early fees for being late, fees to store, fees to offload certain items. Fees for it being busy time of year.

She has commented that even though she has had to decipher some counties where it is not published in English, some of those are easier to interpret than the US version.