One of the dangers of media buys and pre-paid CPA deals IMO is that both sides have expectations and finding the middle ground is not always an easy task. I’m surprised in this day and age that CPA is still around to be honest as it must be more of a pain to manage because of this expectations thing.
It also provides incentive to the less ethical webmasters (not suggesting for a moment that’s the case here) to conduct spam campaigns, dodgy SEO practices and the like which all helps to give the industry a bad name.