As I understand it, Oxfam staff are meant to write the price of the used books they sell, in soft pencil, inside the book. Many branches of Oxfam do, and all I need to do post-purchase is to get my eraser out, and the book will look fine.
Some of my local branches, like the big one in central Manchester, use sticky labels. You know, the kind that divides into three or four pieces, in order to prevent shoplifting. The ones they use are particularly sticky, and for good measure they use two per book. One on the outside, front or back. One on the inside where the soft pencil should go.
Some book covers are strong enough and glossy enough to allow removal of the label without too much damage or difficulty. The inside is another business, and I’ve torn a good many books that way. The very worst is when the book cover is soft or has a matt finish. Then the outside label can’t be removed. The worst I’ve ever had was a really old copy of an Arthur Ransome, where the label ruined the dust wrapper completely.
Oxfam could argue that with used books it doesn’t matter, but I just don’t want an ugly label stuck where it doesn’t belong. If the books were still sold for 20p, my case would be weaker, as it would be really good value (though I still don’t think it’s OK to ruin books), but Oxfam are expensive. Sometimes the books are not much cheaper than the big online bookshop. And if I’ve found an old book, it would be good to have it free from both labels and damaged covers.