Final answer:
A complaint that has regulatory standing is one that is eligible to be reviewed and addressed by the appropriate regulatory authority. In this scenario, the complaint that has regulatory standing is 4) A letter from a customer alleging a trade was executed incorrectly.
Step-by-step explanation:
A complaint that has regulatory standing is one that is eligible to be reviewed and addressed by the appropriate regulatory authority. In this scenario, the complaint that has regulatory standing is 4) A letter from a customer alleging a trade was executed incorrectly. This complaint involves a specific action or transaction that may have violated the rules or regulations set by the regulatory authority governing the financial industry. It requires investigation and potential intervention by the regulatory body. The other complaints mentioned, like voicemails and letters expressing dissatisfaction with an adviser's attitude, may be important for the company's internal policies, but they may not hold direct regulatory significance.