An It's Complicated! — Book Covers guest post by Joseph Monti, a once bookstore buyer, editor, and now prominent literary agent at Barry Goldblatt Literary.
I'm writing today, discussing middle grade and young adult book covers, as a former children's fiction buyer at Barnes and Noble, Inc., and thus this is not wholly my opinion, but also fact based upon sales numbers at the largest bookstore chain in the world. That said, I am not speaking for the company in any capacity, just my personal experience.
The simplified truth to the quandary about book covers is that good covers sell books, and bad covers hurt book sales. A good book with a bad cover may overcome it, but it will not reach the sales potential it could have had with a good cover. A mediocre book with a good cover will increase sales. The marriage of a good cover and a good book is what I am going to showcase.