> 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.

Not comparable. The markets can still charge wherever they want, but it needs to be priced per item and not per customer. In your house counterexample, you could set whatever list price you want.

> 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?

Yes, you should be disallowed. Otherwise every online store will upcharge you based on IP. There can be exceptions for small businesses or individuals, but that's it.