Car Demon has a wide variety of PHP constants that can be used to modify functionality.
Over time many of these constants will be turned into settings that can be adjusted on the settings page. In the meantime you can define these in your wp-config.php file right above where it says:
/* That's all, stop editing! Happy blogging. */
CD_DEFAULT_LOCATION_SLUG can be used to change which location is considered the default. Let’s say you have 2 locations, “Joes Cars” and “Jills Cars”. You can make “Joes Cars” the default by define it’s slug with this constant. Any vehicle that does not have a location assigned to it will automatically be considered a part of the “Joes Cars” location.
To do this you would add the following to your wp-config.php file:
define( 'CD_DEFAULT_LOCATION_SLUG', 'joes-cars' );