public function isValidChargeCode($chargeCode)
    {
        $isStandard = in_array($chargeCode, $this->standardChargeCodes);

        if ($isStandard || Mage::getStoreConfigFlag('doghouse_eparcelexport/charge_codes/allow_custom_charge_codes')) {
            // Charge code not found in the standard list of codes, but system config tells us this is OK
            // @see https://github.com/fontis/fontis_australia/issues/39
            return true;
        }

        return false;
    }