A lie-detector test, administered by an independent party (retired FBI or police and certified), is a great way to prove claims.
As far as these tests go, they aren't that accurate. If someone is of the proper frame of mind, they can pass them with flying colors. I am not trying to imply anything, however, if a psychopath has one of these administered, I would bet they would be able to lie to you and the machine and nobody but them would be the wiser.
Again, I am not implying anything, just saying that these tests assume normality in an individual across a broad range of attributes and people can vary enough to make them worth less insofar as accuracy is concerned.
I also think these polygraph promises are lame. Who cares if someone thinks someone else is on roids. There is no way in hell you can do any better with this contest than to take people at their respective words. If people can't do it, don't have the contest. No matter who wins people will bitch, and if you think the accusations are bad now, wait until the conclusion of this.