None of the above. All of the above. BUC can be useful for smaller boats but I definitely would make no decisions based on it. Soldboats may have weaknesses but it's still by far the best resource I'm aware of. However, I also use the knowledge of industry professionals.
Then it comes to willing seller and willing buyer. Condition plays such a major role and you just have to judge what is reasonable as an premium or deduction based on it.
So much is difficult for those not in the market every day to predict. The market swings. Location plays a significant role. Even currency. A year ago, used Hatteras boats were being grabbed very quickly and shipped to Europe. They weren't that negotiable. Six months ago that slowed down as the Euro dropped. Now it's recovered a little, but more recently the drop of the GBP has played havoc with UK built boats. Within the past two months I've seen some used models in the US priced above what a new one could be purchased for in the UK.
I have a friend about to buy a Lazzara. He missed on a couple. He wanted under 70'. The only one in the US was on the Great Lakes. Now he starts thinking of going a little larger and there are a couple. What happens when a company stops building a boat? Who knows. With one the price rises and another it drops. I would think Lazzara would drop. But not in the smaller sizes where quantity is so limited. There was a period between 2008 and 2011 in which very few Sunseekers were imported into the US. The ones I saw on the market were moving quickly at asking prices. There were dozens of the same boat in Europe that were selling far cheaper.
The one thing I've seen in this market is that for a quality used boat, well maintained, in very good condition it is a seller's market. They'll move quickly at solid prices. For a lesser used boat of the same year and build, but not maintained as well, with quite a few cosmetic issues, it's a buyers market. They start out overpriced, they sit, the price drops, and ultimately they're open to any offer they can get.
If you're willing to do a rehab project a lot of choices out there and price very negotiable. However, if you want a turnkey, move in ready, boat in pristine condition, if you see one you like, you better move quickly.