Does anyone know if there is a web site that tells you how many of a book habe sold? Also I want to know if there is a rule regarding cpmparitive titles? I noticed under the comps titles thread someone said you should not compare to a high selling book?
The simple answer to the first part of your question, Debbie, is no, unless you fork out loads of cash. This data is at the core of the likes of Nielsen BookScan's business model. They will do everything in their power to ensure it isn't available. Likewise, Amazon, as the market-dominant digital book channel - with their own publishing arm! - don't want others using data that is so valuable to them. (Indeed, even as a traditionally-published author, getting your own sales data from Amazon is nigh on impossible.
As to the second, it's not that you shouldn't use books that did well. Indeed, you don't want to compare yourself to books that bombed. It's that you should avoid those runaway mega-hits that buck all the trends in publishing numbers. Comparing your work to a book that sold millions in the first week (when 5k will usually get one on the bestweller list), will come across as concieted; the inference agents will draw is that you beleive your book will likewise be a runaway mega-success, whatever your real reason for choosing that comp.