To give some context, I was a real estate agent in Louisiana, working as a property manager, for some time.
> Can you define the "long period" or point somewhere in the article or other source where this is described?
The article mentions that landlords are using the software to run at lower occupancy rates to increase revenue. One specific landlord was mentioning an occupancy rate as low as 95% on 50,000 units (which is quite low). Landlords don't base occupancy rates on short-term vacancies.
> I probably did not read the same text books you read.
The article describes a service that takes private pricing data from numerous competitors, then gives all the competitors pricing and occupancy recommendations as a means of maximizing revenue. There's a good quote in the article about replacing the word algorithm, with a "guy named Bob". If a person was doing this, it would obviously be collusion, because it's a practice that is already illegal, essentially everywhere.
In real estate school, they were pretty explicit about not even walking the edges of collusion; for instance, simply saying "we only price our commissions at 3%" in a room with other brokers could be considered collusion.
> Do the house sellers who hire the same appraiser also collude in your text book? What about people who use Zillow's or Redfin estimates?
An appraiser sets prices based on factors like recent sales in the neighborhood of similar properties and property sizes, age/condition of the house, etc. Everyone can use the same appraiser because that appraiser isn't doing any coordination across the sellers. Two different appraisers, for the most point, should be setting very similar prices.
It could very well be collusion is every broker was using Zillow or Redfins estimate's, especially if they were giving recommendations on holding properties off the market in a coordinated way to maximize profits.