Assuming this is a legitimate deal.
How much negotiating room do you think there is on a $3,900 boat that may already be grossly under-priced?
Under-priced...? or over priced. The only individual who has ANY idea how the $3,900 price of this vessel relates to its VALUE is the seller, and he ain't talking.
To suggest that this low price means the price is less than the value is a totally speculative opinion. Sellers have close to perfect knowledge of the boat, and what its value really is...they will usually set an asking price above that value to satiate the bargain-hunters. The lower the value of a boat, the more likely the asking price will be well over that value, as the seller can count on certain individuals figuring a low price means they can't lose...
Suppose you own a 40 year old 33', and you know: that the diesel has low compression, there's delamination in the decks, the rudder bearings are shot, you are snipping meathooks off the standing rigging, the sails are threadbare, the cushions deserve recovering, and the instruments don't work. A similar vessel in all good working order is worth $18,000. You know it would take $30,000-40,000 to get your example into that same good working order. What do you do...you ask $3,900 and hope some bargain-hunter will come by, pay what you know is a windfall, while the buyer thinks he is getting a "good deal'
A good deal when buying a boat is to actually get what you pay for.