'create-product' => array(
  'operations' => array(
    'create' => array(
      'help' => t('Add Product'),
      'file' => array(
        'type' => 'endpoints.inc',
        'module' => 'custommodule',
        'name' => 'custommodule',
      ),
        'callback' => 'custommodule_create_product',
        'args' => array(
            array(
                'name' => 'appID',
                'type' => 'int',
                'description' => t("App ID"),
                'source' => array('data' => 'appID'),
                'optional' => FALSE
            ),
            ...

// ...
'access callback' => '_example_resource_access',
'access callback file' => array(
  'type' => 'inc',
  'module' => 'example',
  'name' => 'example.resource-access',
),
'access arguments' => array('foo bar'),
'access arguments append' => TRUE,
// ...

function _example_resource_access($op, $args = array()) {
  if ($op == 'foo bar' && !is_numeric($args[0])) {
    return services_error(t('That is not an integer.'), 406);
  }
  return TRUE;
}