Boats and real-estate are not the same thing, they just cost the same.
What I mean is that even someone that needs to off-load a house quickly and realise some income from it (motivated seller) has options that a boat owner does not. Anything from leasing out to getting a bridging loan or flexible mortgage, until the property can be sold.
This buys them the breathing room to hold to their prices and get what they ask (just maybe a bit later then sooner).
Boats do not work that way. Getting a loan/mortgage based on a boat ownership is *interesting* (see; nigh on impossible at anything other then ruiness interest rates).
A house that gets left sitting for six months still looks like a house, just one that needs a spring clean. A boat left totally ignored for six months *can* turn into a write-off. They lose value far faster when upkeep is neglected (mind you, they also exist in a far harsher climate and move around ALL THE TIME when in the water)
Marina or hardstand fees make the interest rates acrued on even the most harsh of bridging loans look like loose change. So there is a lot more incentive to "just sell it" once the desicion to sell is made.
Unlike most real-estate however, you often hit the emotional baggage and strong "attachment" to the boat of the previous owner, so being prepared for way more BS then you have ever had to deal with in order to give someone around 100 thousand dollars will be an issue. Be prepared to force yourself to be amused by it, or only deal with a broker that really gets between you and it.
We decided to pretty much not use a broker at all, dealt directly with the former owner, got about 400cubic hours of "stories" but also learnt a lot, got handed truckloads of extra gear and found it to be a useful if somewhat tiring experience, but at least the sellers finally got "closuer". We still exchange the odd freindly phone call two years later, just to see how "the boat" is going.
What all the above is trying to say is that you should offer what you think the boat is worth, or maybe a little less and see if they go for it. You can try tactics like concluding what it is worth and then offering a lot less and then climbing in increments until they say yes or you hit your mark, this seems to sometimes work. Just remember, the worst they can do is say no to any individual offer, You can keep coming back with more offers or can go find another boat. Forget getting a "positive" response from the broker taking the message to the buyer. He would really be positive about it if you offered twice the asking price and his commission reflected this!
He is the middle man, the carrier-pidgeon of the exchange, your job is not to make him feel warm and happy.
Most important thing to keep in mind;
You are not trying to make friends with the broker or the owners. You are trying to buy a boat. Remember this as they try to manuevure you with social and emotional levers. You are not applying to be their friend. You do not want them to talk nice about you to all their broker friends etc.
(Oddly enough, if you do a deal that completely screws them to the wall, most brokers will speak of you with a kind of awed respect, if you give them exactly what they want, they will laugh at you and feel superior..after you have gone, of course.)
Having said all that, inviting the former owners out for a sail and a meal on board once you have gotten settled is a good way of learning something extra about your boat and you can at that point decide whether you want to be friends with them. But not before!
It is also advisable to have a sweetener held in reserve that will break a "near thing" in negotiating a price. For us it was "if we get this wrapped up before 3pm, we can do this in cash, today, right now."
So for us, having the loan part of our boat''s price sitting as pre-approved funds in the account was a valuable bargaining tool and well worth the few dollars extra it cost to process the loan that way.
Anyway, hope that helped get you looking at things a certain way.