Advantage Media Management, Inc. advises advertisers that there are 3 things they need to constantly be asking themselves about their media expenditures:
 
1)  Do I trust that the people that are placing my media are doing the best job they can?
 
2)  How do I know I'm getting what I paid for?
 
3)  Am I paying too much for my advertising compared to others?
 
As long as you're asking these questions and taking the steps to make sure these questions are answered (work with a 3rd party auditor), you can sleep soundly as an advertiser.