Visibility of availabilities in the plan viewer can can be turned ON or OFF.
This is specifically useful to align with different sales strategies. In presale, developers might want to hide how many units are actually sold. Alternatively, when developers are confident in their sales, they can show how few units are left to increase pressure on prospective buyers.
You can also choose between 3 states for a specific unit in the Unit module: available, sold / leased and reserved.