It's going out of style, but it used to be that on your birthday, your friends would wish you "many happy returns of the day." I assume that means many more birthdays, but I confess I'm not sure, as I've never heard that phrase used for anything else but birthday greetings.
Returns in the print book world are a bad thing. If a bookstore doesn't sell all the copies it has of a given book after a specific amount of time, the bookstore can return those copies to the publisher for full credit. Supposedly, this practice started during the Great Depression, when bookstores were reluctant to buy stock if they were stuck with it for good because almost no one had any money. The practice of allowing returns is still with us, and it's one reason why it's hard to make money publishing books. But in general, the concept of returns doesn't apply where ebooks are concerned. The beauty of "digital stock" is that it's delivered when it's ordered by replicating a single copy.
However, in a click-to-order world, it is possible to buy something by mistake. And most vendors will accept the customer's word and refund their money if they report a mistake. The Kindle Direct Platform lets authors see right away when then sell a book, but it also shows when a book is returned. It just happened to me! Usually the "Units Refunded" column is zero, but this month someone returned a copy of No Safe Haven. I can't imagine why! -)
Actually, this is a pretty rare event because ebook vendors allow downloading a free sample before you buy the book, so generally, people who buy a book want that book. But now I can tell that return is going to eat at me.
Look before you click, people!