Its called being able to prove that the cop is stupid in court my friends... thats all it takes...
in the states its different than in Canada, as up here, you can't legally pay someone to be a witness or just be in court (which means the cop comes in without pay
For you Americans that get major tickets, research radar a little more, and you'll know more than the majority of cops out there.
link not working, will repost when I find it at home...