There is always the tatty book that's really cheap. Or the rare find that's in a horrid shape. Or the box set that you got cheap turned out to have an oversized box and the artwork on it doesn't match the picture it was sold under but hey, atleast you can toss the cardboard monstrosity and keep the books. That last one happened to me recently. And the first one repeatedly.
I have books where the the covers got mauled by our puppy and I just taped them back together. I've seen nice hardcovers where the previous owners name was scribbled in or even stickered on. I own preowned books that were already cracked at the spine and foxed. Or even badgered. How much are you willing to tolerate? My battered old paperback books are all mixed in with the nice and tidy hardcovers. I've even got unread books that if I don't like them when I eventually read then, I have to toss them in the recyclable bin because they are in such a state.
Does it matter if you settle for less? I've got a friend who is all 'pristine hardcover, don't fold the pages' type. I don't fold the pages, that's not my vice. But the list of accidents that have happened to my books is getting longer each year.
As long as you derive inner help and comfort from anything, keep it. – Mahatma Gandhi
It's nice reading a pristine, clean book, but since I get rid of most of my genre books after reading anyway its not a huge deal. They fall into three categories: Nice enough to sell to a bookstore or ebay, too beat up to sell but in condition to be donated to a charity sale, and actually falling apart, in which case they go to a recycle bin. I actually prefer paperbacks since they're easier to carry and also easier to resell--very few used bookstores in my experience buy hardcover fiction.
A book to read does not necessarily have to be pristine - indeed, some of my old books have got several different "defects" (traces of chocolate, drinks, loose pages) ... but that's my own stuff. I just don't like to read used books in such a condition. Some years ago I rediscovered how magnificent beautifully crafted hardcover books can be (e. g. The City of Dreaming Books by Walter Moers or Good Omens by Neil Gaiman) and since then my bookshelves get overcrowded. However, I won't dump my first copy of Lord of the Rings, regardless how tattered it will get.