Whilst we are on the subject of DHL, I have always been hit with customs charges / handling charges from DHL (even on free samples, which got rejected), but very very rarely from any other i.e. FedEx, does everyone else have the same perception about DHL always charging this extra?
It is not just you. I believe DHL charges a "processing fee" or whatever they call it for filing the actual customs paperwork for you and getting your item through customs, separately from the shipping fee (which pays only for the actual transportation). They do it rigidly for every package, even if there are finally no customs due, either due to the low value of the item or the item being exempted from customs. That fee can be sometimes more than the value of the actual item.
If you ship by regular airmail/post, you will rarely see this, because most of the items coming by post are small and thus fall under the customs exemption limit (usually something like 200 euro, depends on the country). On the other hand, if your item needs to go through customs, you will have to handle the clearance yourself, the post will not do it - that typically means a trip to the customs office, filing paperwork and paying the fee before your item is released.
Of course, if you are shipping within EU/US, you don't see this, it applies only for items coming from the outside.
I can't speak about Fedex - I have used Fedex only once and paid only the actual customs (they probably included the "paperwork" charge in the shipping fee itself already) and that was ages ago.