Why do people argue these things?

Customer: Why do you have this in the fiction section?
Me: Because it's fiction?
Customer: This is a true story. I saw it on the news. It should be in true crime.
Me: Ummm, I'm sorry sir, this is definitely a work of fiction.

I open up the front cover and show him on the copyright page where it clearly lists it as fiction

Me: It's a mystery about a murder case during WW2 where a man is falsely accused. But it's not a real case, it's made up.
Customer: I'm sure I saw this on t.v. - it's a real story and you should put it the crime section.