So the problem is not that they keep the prices high, but that the cost of not making a deal is neglible.
So the correct action would be to introduce cost for keeping units unrented. Personally I'd go with probabilistic approach and just penalize owning large amount of property because the more you have the higher chance is you are letting some of it go unrented. And property ownership is way easier to check than determining if some property is occupied or not.
> There's already a cost of keeping them unrented - the loss of rental revenue.
Right. And observing the market shows us that this cost is too low.
Why would I ever sell an empty unit if it appreciates in value faster than it costs me to keep it? Provided that I have no better opportunity to use that capital, which must often be the case.
If you need capital it's another story. But even in case of a single home, the fact that you can sit on it for months instead of lowering the sale price means it's to cheap to keep it if you don't need it.
So the correct action would be to introduce cost for keeping units unrented. Personally I'd go with probabilistic approach and just penalize owning large amount of property because the more you have the higher chance is you are letting some of it go unrented. And property ownership is way easier to check than determining if some property is occupied or not.