It seems to me that these days customs has tightened up its procedures or something. In the past I have ordered things (clothing, shoes, etc) from the U.S., and received it without any customs charges. This year I've ordered from the same company 2-3 times and got hit with a 40 000 won customs charge each time. I imagine there is a cutoff below which you won't get charged (maybe under $50 or something like that?). Maybe your order was just over the limit so they didn't charge you even though they could have?