You may want to consider contacting Boat US Valuation Services as they will provide no charge current value estimates of the boats you are looking at. They use their most recent survey and insurance data as part of the source. I was very suprised at the large difference (much lower) between their market value and a few seller asking prices.
Establishing the value of the boat, at least to you, is key. Any purchase price less than or up to that value is good, after all you are looking to buy what should be a treasured personal possession, not to make $$ by flipping a one-time steal.
To establish value you need to know what 3-4 examples of the same boat sold for and be able to adjust their prices for condition and equipment. this can take time and until you have established this knowledge you need to be comfiortable with other people buying a boat out from under you - that's OK you learn something from it and can get ready for the next one.
If you want to enjoy your boat ownership, release any expectations that it'll be a good financial opportunity. Boats are called "holes in the water in which you pour money" for a reason.
I offer these guidelines:
1. the best you can hope for in buying a boat is at least get what you pay for.
2. the cheaper the boat is, relative to others, the more expensive or less satisfying it will turn out to be to own.
3. remember the seller has perfect knowledge of the boat, its strengths and problems. You will at best have less or much less knowledge, only good surveyors (hull/engine/rig) get you close.
4. when you see the boat you really want to own, be willing to make a fair offer, negotiate up to your determined value as needed, then enjoy your new pride and joy.
5. If someone makes a killing in a boat sale, its far more likely to be the seller.