Why would Freddy find Eliza delightful? (Act 3)

The fact that Freddy becomes instantly smitten with her emphasizes the concept of infatuation on the basis of external characteristics. He barely noticed her when she was a flower-girl, but the change in her looks and her talk has made her infinitely more attractive to him. These characteristics make her seem to be of a class much higher than before. The location makes a difference, too; what would a girl like Liza be doing in such a respectable home? Furthermore, the fact that the other characters play her as a cultured woman makes it harder for the visitors to become suspicious.