Detailed Explanation:

Rationale for Correct Answer:The Fraud Examiners Manual (2020) highlights document reviews, audit tracing, financial analysis, and inside witnesses as the primary methods of proving corrupt payments. Secret infiltration is not a standard fraud examination technique; it is more aligned with law enforcement undercover operations.

Analysis of Incorrect Options:

A. Taxation inquiries – A valid method to confirm payment sources.

C. Inside witness – Valuable evidence in corruption cases.

D. Tracing payments – Fundamental audit step in proving illicit payments.

Key Concept: Proving corrupt payments — standard audit and investigative methods.