I love the scene between Lizzy and Wickham. When I first saw P&P2 (my first exposure to the story), I thought Lizzy would -- and should -- give him a set-down from the beginning, but she even suggested that his interruption wasn't unwelcome. She really didn't call Wickham on his lies until the end, and then only when he started in on Darcy.

I think Lizzy's attitude was that there wasn't much percentage in bad relations with Wickham, as well as having good breeding, as you say, but she wasn't going to let him get away with implying that an honorable man had behaved dishonorably.

I can't help wondering where that good breeding came from. Not from her parents, certainly. I think exposure to the Gardiners on extended visits from London, combined with her own good character, may be the answer, but as far as I know, we aren't given a definitive one.