My books are in good condition, and I am careful with them. But I am a person that likes to look at them, it helps to remind me about the stories just by looking at the book cover
Also the wallets I've seen are quite good quality, and come in lots of different sizes for a neat fit. And despite being careful I have had books get worn looking if I've read it a few times.
I've found a site that sells the wallets for 40p each which I think is reasonable