Even if there was a book it would have no meaning as the subject is so complex.
I have just tonight looked at a new boat educed from £358k to £208k and that was a sailing boat!
One broker told me that the first offer they ever receive on a boat is about right - the owner then has to adjust.
Currently it is a buyers market but just like houses many owners would prefer to hold on and not sell. Yet the cost of boat production is IMHO set to rise sharply.
What has always been true is that the price you see advertised is seldom if ever the price that the boat sells for. The real selling price os often well below that.
When I sold my last boat it was sold some £90k less than what the others of its type with a lower spec were listed at but they did not sell and are still there.
Yet I also know of someone last week on a roughly 30 foot power boat who seems to be getting his asking price.
There are going to be some real bargains around this coming year as the sales peak has not happened in the Spring and cash flow will become king.
All of the above is just my opinion - its a good time to be looking to buy.