answer: #Person2# forgot to take the dictionaries he bought and comes back to get them. The lady who served him couldn't recognize him until he puts on his hat.
documents: #Person1#: I bought two expensive dictionaries here half an hour ago, but I forgot to take them with me. 
  #Person2#: Who served you, sir? 
  #Person1#: The lady who is standing behind the counter. 
  #Person2#: Which books did you buy? 
  #Person1#: The books which are on the counter. 
  #Person2#: Did you serve this gentleman half an hour ago, Karen? He says he's the man who bought these books. 
  #Person3#: I can't remember. The man whom I served was wearing a hat. 
  #Person2#: Have you got a hat, sir? 
  #Person1#: Yes, I have. 
  #Person2#: Would you put it on, please? 
  #Person1#: All right. 
  #Person2#: Is this the man that you served, Karen? 
  #Person3#: Yes, I recognize him now.