This is a recurring theme, so I'll generalize the interaction- it always runs the same course, regardless of what the person is asking about.
customer: I'm looking for (a subject/book/author)?
me: Okay, if we have (the thing you're looking for) it will be in this section here.
customer: But, I'm looking for (repeats request for subject/book/author).
me: Mmmhm, we'd file that in this section.
customer: Uh, but I'm looking for (elaboration on previous request).
me: Yes, well if we had anything about (the thing you're looking for) it would be right here in this section.
customer: But, do you know what I'm talking about?
me: Yes, you're looking for (subject/book/author), and we would file it right here, in this section.
customer: Oh. But wouldn't it go (somewhere else)?
me: No, when we get that (subject/book/author), this is where it goes.
customer: Are you sure?
And no, I'm not exaggerating for effect here....