You can prevent double booking of a location or facility by turning on conflict prevention for a saved location. 

 To prevent double booking of a location, facilty, or room:

Login as Administrator > Go to Admin Menu > Locations >  Add a location or Edit a location >
Under "Conflict Prevention Options > Check A and B -> Save

Conflict prevention will now be turned on for this saved location.
 

 Add an event at a location via:

Click + to add an event > click [More event options...] > click  Location tab >
Select location for the location drop down list > Save

More info:
Saved locations contain fields specific to a location, e.g. address, state, zip, directions, phone number as well as map and weather links if desired. You can filter events by saved locations in the main calendar view via a location selection list. The location selection list  will appear only when you've added a saved location to your calendar.

The number of Saved Locations that can be set with conflict prevention is equal to the number of categories allowed for the purchased subscription.  If you wish to upgrade the number of locations with the conflict prevention, please email support at support@calendarwiz.com