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They were in fact very fine ladies; not deficient in good humour when they were pleased, nor in the power of making themselves agreeable when they chose it, but proud and conceited. They were rather handsome, had been educated in one of the first private seminaries in town, had a fortune of twenty thousand pounds, were in the habit of spending more than they ought, and of associating with people of rank, and were therefore in every respect entitled to think well of themselves, and meanly of others. They were of a respectable family in the north of England; a circumstance more deeply impressed on their memories than that their brother's fortune and their own had been acquired by trade. (4.11)
The Miss Bingleys may think a lot of themselves, but we know better: their fortune comes from "trade," i.e. business. They may be sophisticated and well-educated, but when you come right down to it, they're not higher ranked than the Bennets—they're just richer. In fact, you could almost say that they're lower ranked than the Bennets, since as far as we know all the Bennet money comes from land. (Confused? Yeah, it doesn't make much sense to us, either.)
"Do not make yourself uneasy, my dear cousin, about your apparel. Lady Catherine is far from requiring that elegance of dress in us which becomes herself and her daughter. I could advise you merely to put on whatever of your clothes is superior to the rest—there is no occasion for anything more. Lady Catherine will not think the worse of you for being simply dressed. She likes to have the distinction of rank preserved." (29.6)
In other words, Lady Catherine likes to look socially superior to her guests. That's a bit vain…
"Certainly, my dear, nobody said there were; but as to not meeting with many people in this neighbourhood, I believe there are few neighbourhoods larger. I know we dine with four-and-twenty families." (9.25)
Mrs. Bennet is insisting that there are plenty of people to hang out with in the country (as opposed to the town), but the subtext here is that only certain people actually count as "people." And Mrs. Bennet's standards are a lot lower than Darcy's.