Unfortunately the only way to really know is to have a PPC expert audit your account. IMO having a good in-house PPC person is crucial, or at least go through a reputably agency (as an in-house PPC expert can be pricey.) Even though agencies charge a service fee, your results will almost certainly outperform just using Google's in-house service or doing it yourself. There are also classes some people offer on the topic, which can help you tell if you are being had. I'm not saying it's going to happen every campaign, but it is a common practice.