The drush command 'rets-import' could not be found
The file that integrates DRealty with Drush drealty.drush.inc is kind of in an odd place within a drush folder of the module.

http://cgit.drupalcode.org/drealty/tree/drush/drealty.drush.inc

Drush will scan the root level of a module folder or your .drush directory for drush include files but I dont think it will randomly scan deeply into module directories. I recommend moving this file into your .drush folder and clearing the cache, then trying from your site folder again. Eg,


cp ./drealty/drush/drealty.drush.inc ~/.drush
drush cc drush
cd YOUR_DRUPAL_PROJECT/sites/all/modules
drush -u=admin -d rets-import