Chris Voss talks about this in his book "Never Split the Difference".
He advocates for teams of people handling a negotiation with the most experienced negotiator just observing.
The reason: it's incredibly difficult to be process, crafting and delivering responses in real time. If your primary goal is to observe the other side, that should be your sole focus. It's also incredibly valuable to have that observation hence why you should negotiate in teams (or at least pairs).
>she would always sit in with another interviewer and never ask any questions of the candidates. She would just observe.