This is precisely what happened. Quoting from my comment at the time (https://news.ycombinator.com/item?id=39579488) --
Subscribing to a pricing data service: legal.
Using data feed to guide pricing and set initial figures: legal.
Agreeing, either implicitly or explicitly, to let the pricing data feed set the price floor: collusion.
Leaving units unsold and refusing to lower the price despite insufficient demand: usually a bad business decision, possibly indicator of a market failure.
Leaving units unsold to maintain agreed-upon price floor despite insufficient demand: collusion, market manipulation. Congratulations, you are a cartel.
[–] DANmode 19 hours ago
Almost always.
The trick is figuring out where the failure is coming from, and whether your society can find a lever to pull to fix it.
You're assuming they were the first kind of fools rather than the second kind.
> Leaving units unsold to maintain agreed-upon price floor despite insufficient demand: collusion, market manipulation. Congratulations, you are a cartel.
Which is the thing that doesn't work when many other landlords aren't in on it, because then they get to fill their vacancies while you're stuck with the empty units.
Notice also that antitrust prohibits attempts to monopolize. Fools are quite capable of doing something which is still a violation of antitrust laws despite being ineffective and unprofitable.