But why do you think that they are doing that? It seems that they are adding customs charges of which there aren't any. I really do not understand it. 

Some other people have said it is for paperwork, but what paperwork? Filling in a three second customs form?

I really don't get what the purpose of it is, or the reason for it.

I do know that lots of American sellers have been convinced that the 'furriners' will cheat them if they don't use it.