It is customary for the buyer to either approve of the sellers contract, or write one up, or make one together if that luxury is available, based on your observations you may make a reasonable offer but try to include language in your contract including dates for retun of deposits, final date of payment for boat, and things like upon suitable survey, and suitable financing,and proven operation of...ect...equipment you think is critical to your offering price. try to protect yourself as much as possable, yet still provide the seller with some protection that you are serious about the vessel and if what theysay is right and wrong with the boat proves true that you will meet your end of bargain. Love is a two way street and selling a boat/buying, is alot like a divorce and shotgun wedding at the same time haha