If you collect books online, you are going to end up with some ex-library books. There are some simple steps you can perform to preserve the book's value.
So you've received your book. The condition looks good, the cover is intact, and the binding looks strong. The only problem is, it's an ex-library book.
Library books are common in the new and used book selling marketplace. They are inexpensive to source, and a lot of times can be very rare and valuable books.
But library books are covered with stickers, and checkout card holders, and stamps. And they have a plastic slipcover and it's taped to the original cover protector. Is there anything you can do to minimize the reduction in value from these things?
Normally, I would just recommend being conservative. The damage you can do removing some of these things is a lot more than the potential improvement in value. The card holder, in particular, is generally glued in place, on a paper page, and tearing that page will change the book completely
If you insist on trying to get the library pocket out, you can try products like Undo label and tape remover. Sometimes heat will help, and you can use a hair dryer on low to warm areas up. But you also could burn it if you overdo it. A product called Cleaning Pad can help in removing residue. You can also try a rubber eraser. Everything that you remove is going to leave some amount of adhesive residue.
The dustcover is generally a bright spot in all of this as it has been covered in a mylar or plastic all of this time. You'll generally notice it's extremely yellow, and it's brittle as well. It is difficult to remove, but since you're not loaning this book out you can save your preservation methods for the paper underneath rather than the plastic itself. You can razor off the tape, remove the plastic, and then get to work on the tape that is attached to the dustcover itself.
There's very little to be done about ink stamps and that's what makes all of this sometimes not worth doing. You can remove the library pocket, you can remove the cover protector, you can get the adhesive marks off, but in the end these are ink stamps that have likely been there for decades.
Is it worth trying to remove them? That depends on your confidence, and the value of the book. If you are using the book as a listing to drive down other listings, it's not the most important thing for you to do. But if you plan to sell this book, and sell it for a premium, it's something that you should probably attempt at least once on a less valuable book.
The first step is try an eraser. If the stamp wasn't particularly moist and didn't penetrate deeply into the paper, this can remove the stamp. It's unlikely that this will work, but it is the least damaging to the paper and the first thing you should try. Also it will give you an idea of what the next things that might work will be.
Once you've given up on that, it's time to try sandpaper. It sounds crazy, but if you use a very fine grit, something around 200 to 400 grit and are quite gentle. You can see very quickly whether sandpaper is going to reduce the visibility of the stamp. You can follow it up with an eraser and pad the page that you are sanding with something underneath it. Just do it very slowly so that you don't tear anything.
You can also try a book repair knife. They have them on Amazon and they have them in specialty craft stores. It is a blade, but it is not a razor. As with the sandpaper, gently go back and forth and see what the effect is before you dig in. If it is improved and you get to the appearance of ink to fade, follow up with an eraser.
If you get adventurous you can also try nail polish remover, rubbing alcohol, or even lemon juice to try to remove stains. This is heavily dependent on the paper type and the ink type, and I wouldn't generally recommend it, but sometimes it's worth a try. Especially if it's a book that you're going to keep, there's no reason not to give it a shot.
All of these techniques can also be used for remainder marks on the edges of pages. Specifically, sandpaper is the most likely to work in these cases. It is very much easier to disguise the work on page edges, and this is probably a good spot to try out these techniques in the first place. Make sure that your book is bound and held so that the pages stay in place, and just be careful and take it slow, and your book will look at that much better for it.
On the page Edge you generally will want to use the sandpaper across the entire visible surface so that there is not just one area that is visibly a different color.
Give it a shot on a book that isn't too important, and please let us know your results at firstname.lastname@example.org