What is the difference in matrimonial affairs, between the mercenary and the prudent move? What does discretion end, and avarice begin?

– Jane Austen

Pride and Prejudice, Chapter 27. Elizabeth says this to Mrs. Gardiner, when she labels George Wickham mercenary because he dropped Elizabeth for Miss King who has inherited ten thousand pounds. How does one tell the difference between the mercenary and the prudent and the discreet and the avaricious when it comes to marital affairs, she asks? Elizabeth is calling out the hypocrisy of her aunt warning her the previous Christmas against marrying Wickham because of "want of fortune."