I paid a full (huge)sales tax in NYS at 8.65% when I purchased my boat. You are correct that I probably would receive some sales tax credit if I were to register the boat in Maine and the boat itself has lost value, at least according to used boat guides, just by age. I think , however, that Mainers pay an annual excise tax on their boats as a condition of maintaining current registration stickers. So its a double whammy for them and for me if I have to do it, because my boat will be in Maine more than 60-75 days and have to pay both a one time sales and then an annual excise tax.