Any constraint to provide the requirements of: Expertise, Time, Experience, Objectivity for an activity to be handled by an organisation should determine the need for consultancy.  

The following criteria should be considered for the consultancy cost to be undertaken depending on the property and requirements of the activity during the evaluation process: Credentials, (i.e. AS9100 lead auditor certificate, OHSAS 18001 & ISO 14001 lead auditor certificetes due to indirect concern), Expertise, Experience, Attributes (i.e. communication skill), Availability, Accesibility, References.