Sales numbers aren't available for every book, and I've found the digging to uncover those numbers rather time-consuming. Those sales numbers of course are useful for gauging how well a book sold, and creating a general success-rate when looking at the books an agent has represented. I've taken to using the number of ratings a book has on Goodreads as a vague success-indicator for books. I'm curious if there are more direct metrics available, or even if someone's done the math to find the average Goodreads-rating-to-copies-sold ratio.

(I know Goodreads isn't the be-all, end-all source of book reviews, but it's the site I use most regularly for book recommendations anyway. Also, sorry if this isn't the best sub-forum for this topic.)