claims returned

Today I went to the library to return some books and to pay for a book that was lost. I told the worker that I thought I'd returned it, but I must not have. "Sometimes we do make mistakes," she said, and she went to check the shelf. It wasn't there (I had already checked the shelf).

I had my wallet out and was going to pay. She asked, "Do you use other libraries?" I said, "Yes, but this is the only library where I return things."

She said there's an option called "claims returned," and we could use that option so I wouldn't have to pay. "You wouldn't want to have a lot of 'claims returned,' but one is fine." This nice worker saved us thirty bucks.