I am curious how they determined the subjects tested were bullshitters. Did they get to know them enough to realise they bullshit a lot? Or did they ask them

I am curious how they determined the subjects tested were bullshitters. Did they get to know them enough to realise they bullshit a lot? Or did they ask them if they were good bullshitters? If so, then maybe they missed those who are bullshitters but either don’t know it, or won’t admit to it.