Recently, I have been looking at one product that provides useful sales-related data on any item you want to look up on Amazon. My feeling is that some of the data is extrapolated from sales rankings and other data is based on ratio algos keyed to the software designer's personal sales experience.
These tools sell well and are not bogus, although the black box element is troubling.
Here is a screen shot of the output from one such tool. The analytics are in the box on the right (click to enlarge). This is generated for anything you look up -- with one product exception.
When you use the tool to look up a book, no such information displays.
Makes you wonder.