What is an indicator of suspicious activity?

Large and frequent credit balances on a credit card resulting in request for refunds is an indicator of suspicious activity because it may suggest that the cardholder is using the credit card to launder money or to conceal the source of funds. This is also known as credit card refund fraud or credit card laundering. The cardholder may make purchases with the credit card using illicit funds, then request refunds to another account or in cash, thus transferring the funds to a legitimate or less traceable channel. This activity may also be used to evade currency reporting requirements or to avoid detection by law enforcement or financial institutions.

ACAMS Study Guide for the CAMS Certification Examination, 6th Edition, Chapter 2: Money Laundering Risks and Methods, page 381

Suspicious Activity Reporting Indicators and Examples, U.S. Department of Homeland Security, Indicator 14: Excess Purchases or Transactions2

Credit Card Laundering, Money Laundering Bulletin, Issue 245, October 2019