The document outlines the 9 most common and expensive mistakes found in Google AdWords audits. These include: 1) not tracking campaign results, 2) lacking a clear value proposition in ads, 3) not using targeted landing pages, 4) not writing targeted ad headlines, 5) bidding too high to be in the top spot without optimizing quality score, 6) not using negative keywords, 7) not using dayparting techniques, 8) not using geographic targeting, and 9) not doing A/B testing of ads and landing pages. The author recommends having an audit done to identify any issues and optimize the campaign.