Without that knowledge of yacht worth....surely one couldn't just deduct big ticket item costs eg rigging replacement & motor....which would approximately cost 20-25k for a 38ft yacht. Or does one just bite the bullet and low ball offer them based on this argument?
Here's an example. I went and looked at a 38?r, the asking price was $80K. The owner had moved interstate and the boat had been left sitting in a pen for some time. From watching these particular 38's for a while, I thought one in reasonable condition would be worth around $80K
The boat looked like it needed some love (obviously), but I was told the engine wouldn't start. There was an outboard bracket fitted to the transom (Red Flag 1.) I was told the owner had bought two cheap Chinese starter motors recently. I rang around local services and found the mechanic who had worked on the boat. The engine was actually seized and was only fit for mooring anchor. Quoted $20K for new motor + fitting. My thoughts on value dropped to $60K.
Standing rigging had to be replaced, that was another $10K, so in order to get a fair condition $80K 38, I was now looking at a $50K offer.
The anchor chain had practically become one solid prism of corrosion. $$$ The electronics were completely outdated and needed to be upgraded, realistically another $10K for VHF, Plotter and AIS and Auto Pilot. Offer now to $40K
This was to say nothing about the interior, topsides and hull needing cleaning of the marine forest on the hull, and condition of sails. The broker said the seller would have a conniption at $60K, So I walked away. Broker came back a month later and asked for $55K.. No.
At the end of the day, the price needs to fit into your own value to cost ratio. Even at $40K, it still needed lots of work requiring time and money. It stayed on the market for another couple months and eventually sold I believe for around $45K.
Everyone's cost to value ratio will be a little different. You just need to know a starting point of what a decent buy for the boat you want is assuming it can be sailed away with everything working to a safe condition, what it costs you to get that boat into that condition, should be deducted from the asking price.
Talk to brokers, look at lots of boats to get a feel for what they look like in real life as opposed to pics online. Look at other boats that are similar to your dream boat to see what they offer in comparison. Talk to riggers about ballpark pricing as rig complexity massively effects cost, sailmakers too. Do your homework, use a broker and get a survey.
Best of Luck