That's the reason why the stuff is pointless. Shitty cars are being passed anyways.

"In one study, researchers in Pennsylvania intentionally created 13 defects in a brand new car prior to inspection. Among the many garages they visited, the detection rate of real defects varied widely, from 25% to 54%. Interestingly, while mechanics on average only found five of the 13 defects, they also “found” an average of two non-existent defects."