When I was a teenager, I often "fixed" misshelved books when I found them in the bookstore. Usually this amounted to reorganizing the Star Trek novels that had gotten jumbled up and out of numerical order, but sometimes it meant snatching up a book that was in the entirely wrong section of the store and reshelving it where I thought it should go. This practice was born of an obsessive tendency (which I still have, but which I am now better at managing--yay adult levels of self-awareness!) and a particularly youthful pride in noticing that books were where they weren't supposed to be and knowing enough about where they were supposed to be that I could put them back.
These days I know way more about books and publishing and where misshelved books probably ought to be than I did at thirteen, but while I value that knowledge, I don't think of it as something that makes me a special, special raindrop anymore. Perhaps that is why I almost never "fix" misshelved books anymore. I also know now that while I'm probably right about a book being where it ought not be, I might not be right in my assumption about where any particular bookstore thinks it should be. I've done enough volunteer work in the library to know that well-meaning patrons taking it upon themselves to reshelve books--and getting it wrong--account for many of the books that get lost. I suspect this is true in bookstores as well, especially when you take into consideration special displays and endcaps and the like. Or maybe my ability to leave wandering books alone grew from the delight I take in spotting the volumes that have escaped their homes and trying to figure out how they got to be so far afield.
Probably the most common reasons for a novel to end up resting lengthwise across the top of a row of business books is customers changing their minds about a purchase and not bothering to return the book to where they found it (or not remembering where that was--probably most people don't spend an hour or two in the bookstore every week, like I do). But I have another thought: if I find I need the restroom during a bookstore browse, I set any books I've already selected on top of a row of books that seems likely to remain undisturbed for a few minutes. (It baffles me why more bookstores don't put a small table or chair under their ubiquitous "No unpaid merchandise in the restrooms" signs.) I note the section where I've left them, come back to them after I'm through attending nature, and carry on with my browse. I have never yet come back to find my books not where I left them. If I come across such small stacks myself, I refrain from moving them as I see them as a discrete "I'm just in the loo; I"ll be right back" signal. Perhaps I'm the only one who does this, but I kind of doubt it.
Of course, I still have the odd moment of weakness. The other day I was browsing the Agatha Christie books and noticed that every one was on a single shelf--save one title. As there was room on the first shelf (naturally, since I had removed a few to take home with me), I shifted that title up to join its peers. Can't have the poor thing sitting all alone, now can we? And if I notice one book by a certain author misshelved a few books away from the rest of the books by that author, I arrange them so they are all together. Surely that's just good manners. I once came across an illustrated guide to sex positions in the children's section. That I trotted right back to where it belonged. I don't know if someone was trying to make trouble or simply set it down by mistake, but I like to think I saved somone's mom or dad that day from a conversation they weren't ready to have.
My absolute favorite misshelved book, however, I came across in one of our local Barnes and Nobles: in the sci-fi and fantasy section, a copy of the Bible. I can only assume this was someone's idea of a snicker, and well played you, haha. I almost moved it but then decided, no. It was a curiosity. Let it lie, let the integrity of this store’s particular misshelves stand. I first noticed it seven months ago. It's still there.