Unsatisfactory operation of computer accounting and invoice management systems, is difficult to detect and remedy. Part of the problem is that, once major investment is made in automatic computer billing systems, there is a tendency for staff in this area to be cut and for assumptions to be made about its acceptability and reliability. It is often difficult for staff receiving complaints to personally intervene, for example by correcting the record on the computer, with the result that faulty invoices and statements may be repeatedly sent out month after month, adding to business inefficiency and consumer frustration.