Comment by m00x

The thing is that there is only a tiny portion of houses ever selling at any time. The only ones that would benefit from selling are people who are downsizing or moving away.

If you buy 60% of the properties on market, the rest will see this and adjust their own prices. Usually this only works when the macro is favourable (low interest rates, easy mortgage applications, etc.), but it is definitely a large factor. It sometimes creates a even hotter market, with people thinking that real estate goes up forever, then they sell.

You're right that it's not always large investment groups. Vancouver in Canada had the same thing happen, but mostly from foreign investors and criminals washing money. The latter was facilitated by politicians who cashed in big on this.