Money launderers use high-value goods (e.g., jewelry, art, and precious metals) to disguise illicit funds.
Option C (Correct): Requesting a handwritten receipt for a cash purchase suggests an attempt to avoid record-keeping, a known money laundering technique.
Option A (Incorrect): Buying gold bars with cash and cryptocurrency is unusual but not inherently illegal unless the amounts are suspicious.
Option B (Incorrect): Credit card payments are traceable and do not raise immediate red flags.
Option D (Incorrect): Kimberly Process-certified diamonds are legally sourced, and requesting them does not indicate suspicious intent.