How can I ship to Canada so Buyer pays no Duty?

I've heard how people are getting ripped off with brokerage fees from UPS. If I understand correctly, shipping via US Post Office will not incur fees? I am, however, reluctant to ship tubes this way. I'd probably never collect on a claim for broken or lost tubes.

I also wonder about the other way around, buying stuff from people in Canada. Someone told me you get slapped with a large duty, like 40% of the value of the item.

This is baloney and there must be a way around this.
Appreciate anyone's input.