How does Canada Customs factor in to eBay'd tires though?

Most of the tire "sales" that I've looked at on eBay are USA-based & done by people who (nearly exclusively) use FedEx, UPS, and other couriers. UPS in particular has a nasty ol' sliding scale which they use to determine their brokerage fees.

I imagine that you have to shop very carefully. Once you start adding currency exchange, taxes, duty, and brokerage fees it won't take long to eat up any potential savings.
