IANAL, and perhaps you are but I don’t believe it is 100% legal. Seems like a matter of degree. What the parent is describing could reasonably be construed as illegal signaling and/or pricing collusion if the market is itself the mechanism for collusion. There will be some interesting internal emails.

Good overview of signaling here - https://www.jonesday.com/-/media/files/publications/2016/09/...

I can go to a variety of hotel/airline/retail/stock brokers/etc websites right now and get prices. Why would that be illegal?

Doing it secretly would invite scrutiny and reason to issue subpoenas though.

It wouldn’t be. Using a tool as a collusive mechanism to set prices jointly or create a price floor would be though.

So if these landlords all got together every Monday and discussed detailed pricing / sales info that would be 100% legal?

What would be the purpose of this meeting other than to make implicit pricing agreements?

Does anti-trust law explicitly require a written / verbal agreement or does doing lots of things that looks like agreeing (without actually agreeing) count?

Talking about pricing is fine.

Not fine: “I’ll set my price to $X if you do as well.”

The hard cases arise when this communication is obscured or implicit.

Saying “I’m charging this much because it’s the most anyone will pay so skip the work of figuring out pricing and just charge the same” is legal. “We agree to never charge less than $x” is not. The question is if realpage lead to landlords keeping units vacant when they couldn’t rent them for the realpage suggested price.