I have a similar problem, yet very different.
For me, Canadian buyers tend to haggle the shipping fee, also they tend not to leave any feedback although, at the same time, they tend to e-mail me directly and thank me for shipping the products promptly.
The above problems bug me to no end. Don't they realize that shipping within Canada IS more expensive than shipping to the US? Moreso, even if the cost of stamp is (say) $5 and I charge $7, they discount the fact that I have to buy the box, bubble wrap, tapes, trip to and from the post office, and PayPal fee which I have to pay when I receive payment for the shipping.
Or (this 'only' happened four times), I was told by the bidder that I'm being unfair in charging them in US$ because I live in Canada.
HUH? This is after I clearly stated on the page "price is in US funds"