Where one person plays good, and the other plays bad, such that you
tell the "good" person information that they can then use themselves.
You are caught off guard. What a contrast! Trust may be directed towards
a good person. A technique of trickery, negotiation, interrogation, just
to do info-gathering.
For instance, this can appear in families. Dad be mean, Mom be nice (to
avoid sexism, this can be vice versa). Thus, Mom exerts pressure on the
child.
In fact, I see this as a psychological masterpiece. One pretends to be good, the other pretends to be bad. The human brain will intuitively pick the "better" options even if they serve the cop's needs well. However, two bodies are needed to perform this technique. (This is because humans love comparisons; this is yet another fallacy. Back to the family scenario, even if Mom punishes less than Dad, it's still a punishment, but the brain sees value in not having the worst one: better does not imply good.