I've never had trouble shipping to Canada but I've shipped some things to the UK and to Germany that turned into headaches. Took FOREVER and the buyers thought I'd ripped them off. I had to do a lot of begging to get them to be patient and not trash my feedback. I mail promptly and I really do try hard to make people happy whether they're buying from me or selling to me--I can't help it if the mail systems decide to sit on your package for awhile. I still ship overseas but I have to post caveats all over the page so people don't get their shorts in a wad.

The other issue that comes to mind is that a lot of stuff I've sold isn't, to my mind, worth what it would cost to ship abroad. I guess anything is worth what people will pay but I've still had people get honked off if it costs more to ship than it did to purchase, especially if I already had to charge them extra for oversized mail or if the item was heavy. This applies to intra-U.S. shipping, too. I sold somebody an electronic typewriter for $10 but it cost $60 to ship it to New York. I had it in big, bold, red letters on the page but they still tried to give me a hard time. I cannot imagine what it would have cost if the buyer had been from Sweden, where the thing was originally manufactured.

SOme other issues that come to mind could be that 1) some eBay sellers are somewhat new to the process, if they are not "professionals", and may not be comfortable shipping overseas or dealing with international payments. 2) the paperwork can be a pain if the item has any significant value. 3) insurance claims can be [even more] annoying.