If you are talking about postage quotes from E Bay, that can vary widely because some vendors will charge the actual amount and even add some for packing and handling. Other vendors will just charge a flat rate just to make life simple and hope at the end of the day all the costs come close to being covered. Yet others will discount the shipping or even offer free shipping in the hopes of making a sale, but sometimes they inflate the price of the item to cover this.
I live in the USA and buy some things from Canada every once in awhile. If I physically send payment or parts to Canada it gets held up in postal inspection on the Canadian side and can sit there forever, and sometimes they even try to add extra fees. If it comes from Canada to the USA apparently it goes right through. I don't get it.... It is like we are at war with Canada. One way to avoid the hassle is to ship UPS and skip the post office.... for some bizzare reason that goes right through and they don't even look at it and it also can be traced with a tracking number.
I once had a friend who lives in Geneva Switzerland send me a T shirt as a gift. Somewhere someone ripped open the package, pulled it out to inspect it (I guess?), but they dropped it and stepped on it, crammed it back into the package and didn't seal it back up. Then it got ripped apart by mail sorting equipment because it was half way out of the mutilated package and then they stamped the actual T shirt itself as being damaged and they were not responsible. By the time it got to my mailbox it was a month late and pretty much totally destroyed with a big footprint on it. Cool.
Anyway....
international shipping is pretty much a gamble.....