Do you have any information about the builder? You may not even be able to get insurance on it. It looks home built. I think a fair price if he gave it to you may be to expensive. There is not much info listed and very few photos and the few dont show much. It is not like a house and if any leans are on it you may be responsible for them. It may be a great deal. But you cannot run into this with out all the info. He has to sell it, if it had any value he would not let it go. It is his problem and it will cost him alot to dispose of it and is trying to sell it to get rid of a problem. Dont rush into this as it could cost more than you want. If you cant look at it and get some kind of profesinal advice, walk away. If you have never done this, please get some advice.
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.