Whenever you need to find out what spaces you have available to provide to a customer, you can simply use a list view to filter your vacant offices Here is how to create one.
Go to Space > Products
Create a new List View by clicking the '+' sign next to the list dropdown on the left
Name your list view
Apply the following filters: 'Record Type equals Office' and 'Office Status equals Vacant' You can add more filters if you like, but keep in mind that these will narrow down your results
Customize the columns you want to see in the list view - this is optional; there are some default columns already selected
Click Save as New.
You will have the possibility to select and view this list every time you need to find out what offices are vacant.