Only the customs and revenue dept. of the country the parcel is entering can charge duty and that is assessed by them at entry....companies use a broker to get the proper paperwork through customs and of course there will be tax charged on any "goods and services". It is probably a brokerage fee+ taxes that you are paying not duty+taxes.
...if duty was charged, it would be tacked on on top of the brokerage fee at port of entry. DD ordered me a couple of kits for my birthday from Connecting Threads and she thought their fee was very reasonable, and that they probably do their own brokering in house.