Re: bill of sale??
The boat shouldn't need a bill of sale if there's a title, but the trailer, which if from NJ, won't have a 'Title' unless it weighs over 2500lbs
That will need a notarized bill of sale stating the terms of the sale, your name, the price, and date. They need to know what you paid so they can collect sales tax. The NJ title has a section on the back for this, so for the boat it shouldn't be needed. If your purchase price is too low to believe, they may insist on a bill of sale or notarized statement from the seller verifying the sale price.