Defining services is very difficult since it is such a broad term. Services include the labor and other work provided by outside organizations for fees and related expenses. In most instances, services from an outside organization are procured as a substitute for in-house employee labor, except in the case of independent audits which could not be performed by employees in the first place. The substitution is usually made because the skills offered by the outside organization are needed for only a short period of time or are better than internally available skills. The charge for these services is usually based on the labor hours invested in performing the service. Services include, but are not limited to, management service fees, advertising fees, professional and technical services, temporary help, contract maintenance services, custodial services and security services.