I bought a 14ft tin boat one time from a guy that had advertised it on a buy and sell. I purchased it and got a BOS from him but it had never been registered. The chain of ownership to the best of his knowledge was, a Canadian had bought it and never registered it as it was under 9.9hp, sold it for cash to his grandfather, a US citizen that had a cottage in Ontario. His grandfather passed away and it was left to his dad. His dad after a number of years gave it to him. Try to prove legal ownership!!!! I got a letter from this guy which I had him get notarized to state what he believed to be the truth and one from his dad as well. I was then told by our government that I had to draft a letter essentially saying that I had no reason to believe that there was any dishonesty in the chain of ownership and that I believed the boat was being sold by it's legitimate owner, got my letter notarized and submitted everything and after many months finally got a registration in my name. What a PITA. The OP gives good advice, get this all done long in advance!