Is this not almost exactly what you get on apartments.com or zillow.com by just looking at the listed prices in an area?

I think you might have the problem backwards. Realpage was about buyer collusion, and that wouldn't look any different from the prices naturally just rising in a market with more demand/less supply because even sellers who aren't colluding would still raise their prices if they saw that that was the going rate in the area.

When there are multiple competing factors all influencing price simultaneously it's very hard to accurately determine how much any particular factor contributed, or what the "actual price" would have been without them.

This is actually essentially the problem that justifies markets as an efficient way to arrive at fair prices - it's computationally too expensive to calculate the precise supply/demand ratios at any given moment, and demand can change much faster than supply can adjust (and nobody could ever really know how elastic demand is for things like local housing markets anyway).

So sellers want to respond to changes in demand by raising prices, because the business model of housing rentals is matching short term demand/pricing/risk to long term costs/costs/risk. But every buyer has their own demand preferences and every supplier has a different product with different fixed costs, and everybody knows their own demand preference and ability to provide supply, so the aggregate price a market settles at "collapses" all that information without explicit coordination: https://en.wikipedia.org/wiki/Economic_calculation_problem

If there truly is an increase in demand, as a buyer you probably do want rents to increase, because otherwise you get shortages like in Berlin where there is nothing to rent. So that's why coordinating to withold inventory with other sellers is bad, it creates a shortage anyway and only a small number of participants need to do it to move the entire market

How it works in Victoria, Australia is for renewing an existing lease is you must provide examples of comparable rentals in the area at or above the price you are proposing. And the tenant can dispute with their own comparable if they believe the price is wrong. New listings can be listed at any price.

There is enough turnover with new listings to find the market rate while preventing existing tenants from being screwed over by unreasonable prices.

Australia also almost entirely works off rentals owned by individuals who own 1-3 properties rather than corporate owners so no one landlord has any sway over the market.

A growing body of economic research shows that this allows producers to keep prices high even with lots of competition.

Should rentals be seen as economic opportunities for hyper efficiencies? IE should the market be structured to extract the maximum profit from renters?

Not clear to me that is the right approach, or if owning rentals should be more of a fixed income approach (or even speculative - profits only come from the sale of the property).

We have that in my city. Works great. If your city doesn't have one you don't have to wait for an official one. You can crowdsource rent data.

Al la dc rent registry, which I always thought was ironic because doesn’t this create a database where landlords can consider prices based on others… but I guess it would be public in this case.

https://rentregistry.dc.gov/

I don’t see why rental agreements can’t be registered with the county like house sales are. It would also eliminate the need for squatter laws, as it would be trivial for police to pull up the county website and see who belongs in the home.

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