Is there an official or unofficial source that ranks recent book releases (past 5 yrs) by number of copies sold? This would be a valuable tool to know what exactly readers prefer.
Often I am tempted by a certain book but it helps to know what the rest of the world thinks about that book with respect to other books.
Publishers don't publish sales figures. Therefore they are not available. For anyone.
The best estimations are those like the New York Times bestseller lists (or the equivalent in other countries), which are based on sales figures from a more or less representative selection of stores.
The NYT explain the procedure on this web page: http://www.nytimes.com/best-sellers-books/. Click on "Read a full explanation of our methodology." at the bottom of that page.
Look at the links in the Wikepedia articles referenced in this question: What are the 3 all-time best-sellers in each genre? Might be helpful.
