Our local Borders has the inevitable Starbucks up on a balcony that gives you a magnificent commanding view of most of the store (sadly both science and children's books are out of sight, but you see everyone coming in). When I occasionally sit up there with a coffee I like to play the 'spot the author' game. I've never seen any, but from personal experience, I know what the signs should be.
First, the frenetic scan. Looking through the relevant section for your book. No it's not there. Better look again. Perhaps someone has put it back in the wrong place. No, still not there. At this point there will often be a terrible cry of pain.
Second, should the book actually be present, the author goes into cunning mode. (S)he removes one or two books from the shelves, scans the backs and replaces them. Approximately the third book to be scanned will be her/his own book. This is then put back face forward on one of those piles of some irritating book that no one wants to buy that are very near the author's own. Face forward books apparently sell faster than spine-out, which makes sense. To complete the illusion, the author now takes out one more book, scans it and replaces it before wandering away with highly suspicious nonchalance. Face forwarding is a must, even if there aren't books already face out - the author's book then has to cover up a section of others. The author feels guilty at this point - hiding other people's books - but this is a dog-eat-dog world.
Just occasionally an author can be lucky enough to see someone pull out their book, or ask a member of staff for advice about that section. This has happened to me once. The member of staff recommended something by Bill Gates (what?) I ploughed in 'Hmm, I've read that - it's a bit dull. This one really impressed me, though.' (Pulls out own book.) 'Oh, right,' says the potential buyer. But she is put off by the title, which doesn't sound serious enough for a present for her boss. Oh, well. I retire, feebly pointing that it's still very good.
If you can't be bothered with author spotting, could I at least ask that you check out the Popular Science section. If you see any books by Brian Clegg, feel free to give them a quick look over and pop them back - face forward, of course.
You're very kind.