The way it was explained to me (years after I had the job) is that we got a rating 1-5 from the battery of psych tests and the interview with the shrink. If you got a 4 or 5 you were good to go. If you got a 1-2 you were a no-go but weren't necessarily crazy. Maybe they weren't crazy enough to fit the norm that had been established. 3's were questionable, but could get hired. My best friend on the department scored 3, and all the shrink could say was that they knew he lied or tried to game the system, not that he was unsuitable for the job.
When I took the MMPI it was obvious that they asked the same questions over and over. Knowing that consistency was good, I checked back to make sure I answered consistently. I wouldn't recommend trying to outsmart the rest of a psych eval.