We purchased our boat in 2003 from a private party in Vancouver, BC.
What Bob and Blackfish said is correct regarding no duty in Canada from private sale, taxes paid in your own state and make sure you get a notarized bill of sale. One other thing and we learned the hard way on this. The private party's bank we went to purchase the boat told the private party to not accept cashiers check. So the first trip was a 1800 mile waisted round trip from Wyoming in January. We had been told before hand that a cashiers check would be OK. Had to set up an account at his bank and then wire the money to that account. When we arrived the 2nd time we just transferred the money to his account and received our bill of sale. No problem in returning across border, but rest of trip was a whole nother story. Blew the motor in our astro van just out of Tri-cities, Washington and ended up with a brand new chev duramax diesel and a lot of debt. Drove a total of over 3600 hundred miles to purchase our used boat. NO REGRETS on the boat or the deal.
Jay