In college I used to take psychological studies for extra beer money. The tests would have the standard scale (rate from 1-5 your agreement with statement x), except a random page of each test would have instructions to ignore the prompt, and just to mark all of the answers a certain way. Same concept, weed out the people who ignore the instructions and just fill in random answers.

I always wondered what would happen if I incorrectly answered those questions - would they still pay me? But I prefer cash to the truth