All he has to do is show up and say he saw you doing a wheelie. He is a "trained professional" so his word trumps yours and you get convicted. Sucks, but that is how it works. Your best bet is to just throw yourself at the mercy of the judge and ask for no points and reduced fines. The catch there is that if you do it they will probably laugh at you, but if you pay a lawyer to do the exact same thing they will probably do it. The whole damn thing is a racket.