I love interesting postal markings. To be honest I do not recall in the least who I got this from, but it is a bit of a puzzle.
One stamp says a 10 cents customs fee is to be charged by using a postage due stamp, another says "Duty Free, Saint Paul, MN US Customs"

Anyone have any insights as to what is going on?
Bonus points for anyone who can tell me what the GB CDS cancel cays.