Well.. When i ordered my vest from airsoftgi, my parcel had to be detoured to customs, and it took a day to process it there. When i went to pick up my parcel from the post office, i got smacked with an extra $46.79. but.. That was because airsoftgi sent it with UPS, so i guess the extra paper was because they needed to pay the UPS guy? It was something like that. So if i had known that that would've been the case, i wouldnt have ordered it from over the border. But what can you do?
For overseas, i think the only way it can have a customs cost is if it is checked by customs and the amount of time it takes for the customs agents to process the package? I have not ordered from overseas yet, but me and my mate are making a big group order to EBairsoft.com, so i guess ill see what i get smacked with when that package will get here. Hope that helped a little bit.