This is the real art of buying. Book price is one thing, but one also has to weigh 1. Where book price is unrealistically low, as Spink can be where coins rarely come to market 2. How far above book one is prepared to go, to win something one really really wants 3. imponderables such as 'above average eye appeal' or strike, etc I've been far too guilty in my time of using 'book' as a kind of bible, above which I wouldn't go, and missed some beautiful coins as a result. The example that comes most often to mind is a W&W auction in 1997 or 1998 - one of my first, if not the first - where there was a BU 1873 penny. Book price was then, I think, around £75. I dropped out at that point, and the penny went for over £100 (£110? £120?). Oh why didn't I stay in? I just didn't know, as I do now, that truly BU examples of any bun penny between 1864 and 1881, very rarely appear and are snapped up as soon as they do.