This, combined with Goodreads willingness to let you have the daily ratings statistics on any book for the last six months (though, annoyingly, not any longer than that) means you can generate all manner of analysis. Recently, some publishers have begun to offer their authors access to detailed and high tempo sales data online, but in reality a pretty good version of that is available to Joe Public on Goodreads.
Here are the daily ratings numbers for all 7 of my books for the last 6 months, stacked up in order, with Prince of Thorns at the bottom and Red Sister at the top.
So you can see that around its release Red Sister was outselling Prince of Thorns but that currently Prince of Thorns has regained the throne. You can see that collectively the Red Queen's War trilogy sell around the same as Prince of Thorns does on its own. And by using the ratings-to-sales ratio of 7.7 you can see that I'm selling around a thousand books a day in English.
Do publishers use these sources of data when looking at authors they might want to sign? My feeling is that they don't, but they probably should.