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add_action('pre_user_query','yoursite_pre_user_query');
function yoursite_pre_user_query($user_search) {
 $roles = wp_get_current_user();
 if ( in_array( 'shop_manager', (array) $roles->roles ) ) {
  global $wpdb;
  $user_search->query_where = 
   str_replace('WHERE 1=1', 
   "WHERE 1=1 AND {$wpdb->users}.ID IN (
   SELECT {$wpdb->usermeta}.user_id FROM $wpdb->usermeta 
   WHERE {$wpdb->usermeta}.meta_key = '{$wpdb->prefix}capabilities'
   AND {$wpdb->usermeta}.meta_value LIKE '%shop_manager%')", 
   $user_search->query_where
  );
 }
}