The rules of shelving can seem arbitrary, even arcane, but the fundamentals are easy to learn: two hard covers, and no more than three paperbacks of the same title, on each shelf. The exception is the face-out. If the jacket is displayed horizontally, behind it you can stack as many books as can fit.
Turning a book face out is an act of tremendous power, or so it feels when you are working at an independent bookstore at a moment that has major chains shrinking and Amazon wreaking havoc with publishing’s already fragile ecosystem. In a bookstore, you can decide, unilaterally, without having to ask permission or sit in an hour-long meeting, to simply face out Rohinton Mistry’s A Fine Balance because, well, because it’s one of your favorite books, and it also solves the problem of what to do with the space left by your desire to consolidate the David Mitchells, which means moving them all to the shelf below.