Problems with shipping to Canada

I've been sent alot of packages from the U.S. (I am Canadian) and have ALWAYS paid for the shipping along with the agreed upon price, without exception. I always clarify that I will pay for shiping immediately upon initial contact with the seller (except for one time when a seller/sender refunded the shipping price to me, happy that I didn't try to haggle him from his asking price, a nice surprise.)
I have bought 65lb. amps, 75lb each speakers, cables, c.d.'s, large items, bulky items, heavy items, small items, .... you get the point- I've always used DHL, ground and air, without a dent in my packages. DHL comes highly recommended from my own experiences.
So, perhaps in such situations it's "seller beware" along with "buyer beware". I think it's a good practice to insist pre-paid shipping, too many jerks in this world who are completely ignorant to common courtesy and good business practices.

Keep in mind:
1) A 'certificate of origin' must be provided to take advantage of NAFTA rules (this can be provided from the equipment manufacturer, usually they'll send you one over e-mail, you can then print it- quickest and easiest method)
2)This certificate should be provided by the seller, as it must accompany the package at point of entry into the country. The exception being that the buyer may provide it, if the buyer wishes to clear customs themselves. If the latter is an option, you must clearly state so on the waybill at the time of being shipped. This will save hassles/confusions with your shipper.
3)If picking up or clearing yourself, printing off Audiogon communications between the buyer/seller is a good idea as this is the only real proof of the final selling price. Canada Customs has been this picky- a simple credit card statement has not always sufficed.
4)if you wish to generously donate more funds to our respective governments, ignore all the above and pay duty/taxes.