Probing is when one negotiator “pokes around” to see how to exploit another by learning about their personal issues, or determining their tells and hot buttons. In its purest form, it is simply a valuable skill. In its malignant form, it is used to push buttons and provoke an emotional response.
Interviewers on documentaries want an emotional reaction for entertainment and ratings. They typically probe the interviewee and may put very upsetting falsehoods into the interview to trigger an emotional response. The interviewee, wanting social status or exposure, must react carefully.
The best way to guard against probing is to reinforce your boundaries. Do not empathize with the position they seek. Negotiators know what they are doing and require a crack on the knuckles, not compassion, especially if they are NPD sufferers. With professional negotiators, consequences for trespass work better than understanding.