If a patron gives me the wrong information, it can be very hard, if not impossible, to give them the books they want.
For instance, a patron asked me for books on WWII. So I confirm that's what he is looking for, and tell him where the section is (940s).
About fifteen minutes later, he and his mother come up to the desk. He hadn't known that it wasn't the war that he needed books on. It was WWII weapons. Completely different section.
So I look them up and take them back there. No books checked in specifically on WWII weapons (tanks and bombs, to be exact), but there were to giant encyclopedia's on the shelf on weapons that had what they were looking for.
Another with the wrong information is if they don't have the right title or author for a book, but that's easily fixed. If I don't know it, and can't find it within a handful of different searches, I pop the name and/or title into Google and Amazon and run a search that way.