Last week I learned the power of the handsell.
A woman came in looking for a book suitable for a third grader who had read all of the Harry Potter books. (Needless to say, this girl was supposed to be a voracious reader.)
It turns out that voracious readers are the hardest to buy for because whatever you say, they will already have read it. I know--I'm one of them. So I was racking my brain trying to come up with something the girl would not have read...and then I spotted a brand new middle grade title on the shelf across from me. I hadn't read the book (still haven't, though it's on my list), but I knew the general plot, that it was middle grade, and (most importantly) that it was released just a few weeks ago, thus making me fairly confident that this girl had not already read the book.
I pulled it, mentioned that I'd heard good things but that I hadn't read it, and was about to suggest another few titles when the woman said, "Great, I'll take it."
Boom. Sale made. With those four words, I personally became responsible for the addition of $1.50 (or so) to that author's royalty account.
What readers don't always understand is that there are many people out in the world who aren't necessarily Readers, but who Buy for Readers. The Buyer's greatest resource is the independent bookseller (a clan I recently managed to buy my way into). They want good recommendations, and they want them now. None of this futzing about comparing this and that and the next title.
All this makes the independent bookseller an incredibly powerful person. If they like you, they will handsell the crap out of your book. If they hate you, your book will become mysteriously lost and never ever sell. So authors, be nice to your booksellers. They can be your greatest ally...or your worst enemy.