I'm not psychic

I'm checking on customers when I come across a rather confused looking man. This happens a lot in the computer section and we try our best to help people figure out what they need.

Me: Can I help you find something?
Customer: I'm looking for a book to help me with my computer.
Me: No problem. There are all kinds of books for that. Do you want help with the computer in general or a program?
Customer: I just want a computer book.
Me: Okay. What operating system do you use?
Customer: I just want a computer book.
Me: I know sir, we just need to know what kind of computer book is going to work for you.
Customer: A computer book.
Me: There are different kinds of computers and therefore different kinds of books. You don't have a Mac do you?
Customer: A what?
Me: A Mac - an Apple computer? It's a type of computer. No problem, if you don't know what it is you probably don't have one. You probably have a Windows machine.
Customer: I just have a computer.
Me: Is it new? Did you just get it?
Customer: Why are you asking me all these questions? You don't need to know if my computer's new to sell me a book. I just want a book to tell me how to use my computer.
Me: I'm just trying to figure out what book you need. As you can see (waving my hand at the shelves) there are quite a few different books on computers. If it's new you probably want something on Vista.
Customer: Listen. (Becoming Rude) I just want a basic computer book. I don't want anything special and I don't need to answer all these questions from YOU.
Me: Okay. (I randomly pick out a Vista for Dummies) This is a basic computer book.
Customer: Now was that so hard?
Me: (Biting my tongue) You have a nice day sir.

I found out later that he came back into the store to return the book. His computer was secondhand and quite old so he didn't have Vista and he was trying to figure out how to use some kind of software, not the operating system at all. I tried to help. Really I did. Some people don't want to be helped.