answer: #Person1# recommends a purple dress for #Person2#, who is looking for something for #Person2#'s sister, and tells him the dress can be exchanged with the receipt.
documents: #Person1#: Can I help you?
  #Person2#: Oh, I'm just looking, thanks. Well, actually, I'm looking for something for my sister.
  #Person1#: And what exactly are you looking for?
  #Person2#: I don't really know. A dress?
  #Person1#: Right. Well, what color does your sister usually wear?
  #Person2#: Well.
  #Person1#: OK, what color are her eyes?
  #Person2#: Green.
  #Person1#: OK, purple usually suits people with green eyes.
  #Person2#: Oh, great. Purple is fine.
  #Person1#: Now, what size is she?
  #Person2#: Uhm, well, she isn't very big, but she's not particularly thin, either.
  #Person1#: That'll be a medium then. Well, we have this rather nice silk evening dress here.
  #Person2#: Good. I'll take it. How much is it?
  #Person1#: $70. 00, sir. How would you like to pay?
  #Person2#: $70. 00? Ah, by credit card, please.
  #Person1#: Fine, if you could just sign... 
  #Person2#: Here you are. Goodbye.
  #Person1#: Just a minute, sir. Here's your receipt.
  #Person2#: Oh, yes. Emm, can she exchange it if it doesn't fit her?
  #Person1#: Yes, but she needs to bring in the receipt.