depends on some arcane rules, I believe that NAFTA thing is on stuff made in US, Canada and Mexico but I could be wrong.
My experience has been that the couriers are very good at collecting customs or 'border fees' and that generally the post office does not on used goods. Although they are more likely to the more the item costs and the faster it is send.
Thats just been my experience though.
Oh, and if the courier fee includes customs (bc.com) then I haven't been charged anything.