Obtain the title signed on the back along with a bill of sale. How do I fill this out?What is the process for a boat bill of sale? 1. Enter the seller's name and address. The completed form includes the purchase price, date of sale, a description of the boat, and the signatures of the buyer and seller. A boat bill of sale (also called a boat purchase agreement) is a document used to detail the terms of a transaction between a private seller and buyer. A boat purchase agreement is a legally binding contract between two parties that establishes the terms and conditions governing the sale and purchase of a boat.