Answer: Possible violation of insider information rules or insider trading
Explanation: Insider trading simply buying or trading a public company's stock based on non-public information. In the scenario given above, the client was tipped by a sales representative via a confidential source which hadn't been made public or via legal communications sources from the company.
The prohibition also applies to those who aids and abets a company's insider information leakage as it is deemed illegal. By violating insider information, it gives unfair advantage to those who have access to such information enabling them make more profit.