Public Protector Thuli Madonsela most often deals with overcharging, false billing and misrepresentation of qualifications, her office said on Thursday.
She told the Association of Certified Fraud Examiners (ACFE) this week that she came across these practices when investigating tenders and other state contracts or transactions.
Billions of rands were lost through these practices, with overcharging and false billing incurring a direct loss to the state and ultimately tax payers.
Lying about qualifications increased the risk of poor service delivery or none at all.
She said complying with numerous treasury guides was one way to prevent such loss.
Drawing from previous forensic findings and adapting organisational systems could also minimise fraud and corruption.
"Good investigations contribute to the prevention of corruption and fraud, whereas bad investigations contribute to an enabling environment where corruption and fraud thrive."
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