The blue book is commonly used in the used car market, and is a guide to the trade about where car values sit. I had only assumed that one existed for the used aircraft market, had never actually seen nor heard about it, but if you think about it, one has to exist.
The issue with these trade books, is that the figures are based on depreciation, recent trend sales values, and what the market can expect at any given time. Also, as in any trade, supply and demand will play a large part, access to funding, cost of funding etc.
The market is currently suppressed, no active demand, limited funding availability, uncertainty regarding loan/financial sustainability, rising costs-and the list goes on and on.
The insurance companies will obviously look at this, particularly if and when the time comes to pay out, watch them dive for cover, and the lowest market price, hence the extremely good idea of - over insuring/inflating the initial value- of your asset. They have accepted your valuation when the underwriter signed the dotted line, so it is good practice to go high, within reason of course. You can then argue the toss re the pay out.
As I've mentioned before, I don't think there is a "book" as such here in the UK.
The "market makers" are the small handful of used plane dealers who advertise in the magazines. They know the business intimately and will tell a seller what his plane will sell for if he wants a quick sale, and what it might sell for if he doesn't mind a long wait.
They also know that prices actually paid are a lot lower than those advertised - perhaps 30% lower in the "common type" cases.
And people selling privately thumb through the adverts and base their selling price on the dealer adverts 
In the car trade you have a book because there are thousands of dealers, each with a load of salesmen, many of them not particularly smart, and they need to make it very easy. In fact I think there are several books. For decades, Glass's Guide was the leading one.
I had a peek at that link, Ialianjon.
Interesting, and I note that it is subscribe only, to get the deals. One fairly large disclaimer was that the value of upgraded, and pristine models will significantly increase the price to pay.
Wonder how that would sit with the insurers?
