Make sure your ppc amounts are the right amount. IE, .50 and not 5.00
I did that one time, was a very costly lesson
As far as ppc goes, it might be better to trust noone, but there are a few that give the tools for you to help them find bad clicks. As mentioned above, one day a PPC engine could be gold, and the next they go to hell because of an affiliate or some other variable.