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_CONDITION can be used to define the default vehicle condition. For example, let’s say you only sell “Used” vehicles and don’t want to bother adding “Used” to each one. You can use this constant to save each vehicle with a condition of “Used” without needing to manually add it.
To do this you would add the following to your wp-config.php file:
define( 'CD_DEFAULT_CONDITION', 'Used' );