The Man in a Hat

customer:I bought two expensive dictionaries here half an hour ago, but I forgot to take them with me.
manager:Who served you, sir?
customer:The lady who is standing behind the counter.
manager:Which books did you buy?
customer:The books which are on the counter.
manager:Did you serve this gentleman half an hour ago, Caroline? He says he's the man who bought these books.
caroline:I can't remember. The man who I served was wearing a hat.
manager:Have you got a hat, sir?
customer:Yes, I have.
manager:Would you put it on, please?
customer:All right.
manager:Is this the man that you served, Caroline?
caroline:Yes. I recognize him now.