Working my way through Skyrim for a 3rd time, I have always wondered why all the ruined and burnt books: what purpose do they serve other than as windows dressing and why would anyone want to buy a ruined book (but not a burnt one).
Then, not too long ago, it hit me.
What is one of the necessities in life that has yet to put in an appearance?
Toilet paper!
And there we have a reason why the ruined books are not only desired, but worth 5 gold septims each (or two books in trade for a night's stay at an inn).