In the scenario where users are mistyping the name of a fileshare server, leading to broadcast requests, the most effective exploitation strategy would be for the penetration tester to respond to these requests with their own IP address (D) and set up a service to capture authentication credentials. This technique is known as a "Man-in-the-Middle" (MitM) attack, where the attacker intercepts communication between two parties. In this case, the tester can exploit the misdirected requests to potentially capture sensitive information such as usernames and passwords.