My $.02 here...
If it's a boat you plan on doing major resto/work on, there are a lot of things you can use to your advantage when trying to get a deal (in some cases), and it might work to your benefit to not TELL them you want a project.. For example, if it has an OMC stringer drive(s) and you are willing and able to redo the transom and re-power with newer gear, you should be able to get it for almost free as they arn't worth much, even in good working condition. Same as the 'king' cobra drives, there are literally NO new parts available any more. Also, IMO, you should bring a compression tester when you go to look at anything. There are old motors out there that are in great shape and just purr...and new ones that have had the nuts run out of them and are ready to die. If its on a trailer, check the tires, brakes, lights, and if its an old rusty looking hulk, plan on spending some money there if you're gona tow the boat for any distance. A half decent boat on a craptastic trailer still isn't worth much..
Obviously if the hull is very faded, severely scratched and beat up, showing many many stress cracks, or has transom issues, it can be a good bargaining tool. Everyone likes and wants a shinny boat :lol: and trust me, it's some work to bring back poor care and maintenance on an old hull.
Next would be interior/seating and canvas/top and general aesthetic issues... poor condition here, and worn/dirty ripped and torn fabrics are a HUGE killer on the price of any boat, regardless of age IMO. Mainly because of the cost to re-do and repair (which again, is quite a bit cheaper if you diy)
I picked up my current boat for $1500.. spent 2 months and another $2000 or so, and now I have a great boat that I know everything works on and is solid.. and have had an offer of $10k for... :laugh: So what kind/size/type of boat ARE you looking for?