Here’s a little trick I picked up after watching a store clerk do it.
Step 1: Removing the Label
The secret to removing a label from a book without damaging the book or tearing the label is… lighter fluid.
Put few drops on the label and spread it around. Don’t worry if a little gets on the book itself. I’ve tried this even with non-glossy covers and it caused no permanent harm.
Give it a couple of seconds to soak in, then carefully pick at a corner of the label and slowly peel it up.
The lighter fluid attacks the adhesive without significantly weakening the paper, allowing you to peel up the sticker in one piece, and the discoloration you might see on the book itself will go away completely as the highly volatile lighter fluid evaporates.
(On a non-glossy book, where the entire surface of the “stain” is exposed to the air, it should be gone in under 5 minutes. On a glossy book where some got in through a nick in the gloss or at the edge of the cover, it’ll take significantly longer.)
CAUTION: While I’ve yet to encounter any in use in the printing of book covers, the label on my can of lighter fluid does mention that it will lift “solvent-based inks”.
Step 2: Removing the Residue
Now, you’re left with sticker residue on your book and, since it might not be a glossy book, you don’t want to use a gunk remover which could stain the book.
You can carefully roll most if it up into a ball and then pull it off, but that’s not going to get your book clean in any reasonable amount of time.
Secret ingredient #2: “Invisible Tape” (ie. Frosted Scotch/Sellotape)
If you’ve ever experimented with the different kinds of clear plastic tape, you might have noticed that the adhesive on the frosted tape meant to blend in on paper is significantly weaker than on the crystal clear “Transparent” stuff.
It’s actually so weak that it’s easy to peel off paper without harming it if you can get a peel started without damaging the edge of the paper and that’s the trick: Contact adhesives love to bond to other contact adhesives.
Wrap a loop of the frosted stuff around your finger and repeatedly press-and-pull on the sticker residue until the tape gets exhausted. Depending on how large the sticker was, you may need to switch to a new piece of tape one or more times to get all of the residue up.
As an alternative, if your book cover is glossy and the coating is unbroken, you can also use one of the “home-made Goo Gone™” recipes floating around the ‘net, made from baking soda (as a gentle abrasive) and vegetable oil (to keep the gunk from re-adhering as it lifts). I haven’t tried it yet, but I’m told that Goo Gone’s active ingredient is one of the components of orange oil, so it may be possible to make the homemade stuff with that to rely less on the “scrub with baking soda” aspect.
I’ve tried both approaches to step 2 and was perfectly satisfied with each.
A week or two ago, I used lighter fluid and home-made Goo Gone to remove a strongly-adhered barcode sticker from a copy of Programming Windows 3.1 by Charles Petzold, which has a pure white, glossy cover and it now looks brand new. (I just had to wait longer for the lighter fluid to evaporate after I accidentally let some reach the edge of the gloss and soak in under it.)
Today, I used lighter fluid and invisible tape to remove another barcode sticker from a copy of Microsoft Windows Resource Kit for Operating System Version 3.1, which has a pure white, matte cover that could have been torn by the adhesive if I removed it dry. It also looks brand new despite the lighter fluid initially producing a “big beautiful stain” around the sticker. (Though I did choose to roll up and lift the lion’s share of the adhesive residue with my fingers to reduce the amount of tape I needed to use to lift it all.)
UPDATE: If you’ve got something more stubborn, like a security sticker, and it’s on something more robust, like a glossy-finished video game box, check out the techniques used by Clint from Lazy Game Reviews. (Also includes instructions for building replacement structural support for flimsy game boxes.)