In the final analysis, just like any accounting system (even manual),  measures are put in place to ensure that only "the chosen few" are allowed to make major changes.  Even then the systems can never be fraud-proof, but the protection measures needed make them cumbersome at the operator levels.  
Probably all systems have to face up to the same problem.  Jhb Municipality's (in-)famous billing system is a case in point:  after many years, incorrect data-base entries are still not cleared up - partly at least, because of the higher-up authorisation needed to make corrections: the customer-facing "consultant" can only report the errors for "somebody else" to correct.  Often, the "somebody else" is "too busy".  The blame is often placed on SAP, but in reality it is a "finger problem".