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The chances of passing a "re-test" will vary from agency to agency. For the FBI, the chances are virtually zero. While there may be rare exceptions, it's clear the FBI has made a political decision that applicants who initially fail their pre-employment polygraphs and are offered re-tests (to create the appearance of fairness) will not pass.
But this is hardly the case with all agencies that require pre-employment polygraph screening. For example, its not at all unusual for CIA and NSA applicants to be initially accused of "having problems" with the polygraph and to be eventually "cleared" after one or more follow-up sessions.
And there are local law enforcement agencies that have gone on to hire applicants who failed their initial pre-employment polygraphs but passed on the 2nd or 3rd tries.
For information on how to reduce the risk of having a second false positive outcome, see Chapters 3 & 4 of The Lie Behind the Lie Detector:
I have already failed 1 poly and awaiting a retake...and then I find this site. I have read testimonials and documents and get that the poly doesn't work and it is really more of a deterant and a means to get you to confess. Well...the question is how do I pass this next poly. I read what it says but it obviously didn't work because I got hammered on the drug use question. I guess the mistake was telling them everything that I possibly could remember. None of it applied to the question (they even said that) but I guess that doesn't matter. The only thing I can think of is go into the test knowing that it doesn't work...don't give out any info that can be used against me regardless of the innocence of the answer. The question is though, since I have already failed 1, I fear that regardless of how well I do, I won't pass anymore. I really need this job, so I am totally frustrated at this.