This may not be the model for everyone, but I generally look at a few of the higher priced and mid-priced 'similar' boats. I look at how those boats have been maintained and then I compare them to the one I am truly considering. I take my own pictures of the boat that I am truly interested in, and I do my own sort of quick survey of what it might cost (time & money) to refurbish/restore the boat. If it looks like the cost will run anywhere near or exceed the cost of the similar boats then it might be worth consider the others too. Of course, that's not all there is to it, but that's kind of a basic and way oversimplified version of the mental principle that I use. There's also plenty of gut feeling in it, oh, and don’t discount common sense.
it’s amazing how many people disregard that last little nugget.