I have seen a similar trick described somewhere else, possibly in one of Mark McCormack's books. When discussing a major event with a large hotel, casually ask for orange juice for all participants, freshly squeezed on the premises that morning. If hotel management appears to regard this requirement as trivial, then this is a warning that it may not take the other requirements seriously either.
Obviously these tricks only work when they are secret. As soon as people realise that these tricks are being used as tests or predictors of performance or quality, then they will alter (distort) their behaviour accordingly. (I'm imagining a scene from a Spinal Tap remake in which a rival rock band sends its roadies to tip off the venue and disrupt proceedings, so that the M&Ms are perfect, but the wiring electrocutes the guitarist and wreaks the concert.)
So if you are going to use these kinds of trick as a shortcut to detect what's going on, you need four things.
- to design a test that is a good indicator of incompetence, laziness or inattention
- to behave congruently as if the test really mattered
- to act appropriately when the test fails (e.g. test the wiring, look for an alternative venue)
- to watch out for signs that the test has been rumbled