I think the major difference is price is set at the margin, so only the marginal renter has to use the software in order to move the market. Since rental owners

I think the major difference is price is set at the margin, so only the marginal renter has to use the software in order to move the market. Since rental owners, like wealth, exist on a power law curve large numbers of properties are owned by very few people. I.e. it is possible for both the average landlord to not be using the software but the average property is owned by a landlord who is. The other thing is that normally there is an advantage to breaking the collusion which is what generally prevents them. AFAIK the software is capable of punishing people who break from the suggested price so this pushes the cost of maintaining the collusion onto the participants who have to put up with vacancies for longer than they would otherwise. So in my view you can have an implicit collusion, or a collusion in effect even without an explicit collusion and with most of the participants not participating in it. I also think this is one of the most important points of contention of our time. Our ponzi economy requires extracting monopolistic rents which is absolutely crushing the middle class and younger people. When I last visited SF downtown was a ghost town with many of the businesses that survived Covid being driven out by high rents - it appears that rental collusion has already been more damaging than a global pandemic.