Shipping from Dr. Diff in USA?

I've imported tens of thousands of dollars of parts from the US over the last 25 years. Brokerage and handling charges seems to somewhat depend on the carrier, method of shipment and value but who knows the exact rules. UPS ground always seems to come with high brokerage charges. Often it is still worth it rather than buying from a Canadian dealer (if there is one) who just builds all the charges into the price and then some.