When should a PS Form 8105-B be filed by a sales and service associate?

The correct answer is based on the guidelines established for monitoring transactions that could indicate potential money laundering or other suspicious activity. A PS Form 8105-B must be filed when a customer makes large purchases, such as $1,000 worth of money orders repeatedly within a short time frame, which in this case is suggested as happening every day for a week. This threshold of $1,000 and the frequency of transactions raise flags about the possibility of the customer using money orders for illicit purposes, thereby requiring this form to be filed as part of compliance measures.

The other options represent transactions or scenarios that don't trigger the need for filing the PS Form 8105-B according to the established guidelines. For example, a single transaction exceeding $1,000 may not be enough if it's a one-time purchase, since continuous or repetitive patterns are what signal the need for scrutiny. Similarly, while suspicious behavior can raise alarms, it alone without evidence of significant transaction patterns does not necessitate filing the form. Completing transactions without cash payment does not automatically lead to issues warranting a form either, unless those transactions also meet specific thresholds for suspicion or repeated patterns.