> If I'm selling to the wealthiest zip code, where the median house price is over $10M, should I be disallowed to charge higher prices?

I think so, because perhaps your costs to distribute those products is more too. But what I don't think you should be able to do is say, well your house was $50mm and your house was $1mm so you pay much more. Or you're wearing Air Force Ones so maybe your price is just a little more wink wink. It's a bit like hyper-targeted advertising versus general advertising.

> If I'm posting something for sale on Craigslist, and I don't put a price, is it OK if I quote different prices to different people who text me?

I think so as well. I don't see a problem with this - you don't know anything (maybe besides a green/blue text) anything about the buyer, how much they make, &c.