Skimming cases can more likely to be detected by:

Skimming removes incoming cash before it is recorded, leaving no audit trail against which routine controls or audits can be applied. Consequently, these schemes are most frequently uncovered only when something unforeseen happens—a customer complaint, an observation by another employee, or some other accidental event that exposes cash that should have been recorded but was not.

A. Internal audits compare recorded amounts; because skimming keeps transactions off‐books, auditors usually have nothing to test against and detect few cases.
C. Internal controls relying on recorded data (reconciliations, approval chains) are bypassed when the sale is never entered; preventive controls may deter but seldom reveal existing skimming.
D. “Occupational frauds” is a fraud category, not a detection mechanism, and thus does not answer the question asked.

1. ACFE Fraud Examiners Manual

2022 ed.

Section II – Financial Transactions & Fraud Schemes

“Skimming

” Detection subsection

pp. 2.304-2.305: “Because the transaction is never recorded… skimming schemes are commonly discovered by accident or customer complaint.”

2. Wells

J. T. Principles of Fraud Examination

5th ed.

2019

Chap. 11 “Skimming

” p. 332: “Skimming is extremely hard to detect; many schemes are uncovered purely by chance.”

3. ACFE Report to the Nations 2022

Appendix A

Detection Method by Scheme

p. 96: skimming shows the lowest detection by formal controls

reinforcing accidental discovery prevalence.