Search: Google's Guesswork
The quality score algorithms operate under the assumption that you're an honest advertiser with pure intentions ... or at least reasonably pure intentions. The system penalizes advertisers who show signs of intentionally or unintentionally disrespecting the people who search and click. These penalties can negatively impact the quality scores you'll receive for specific keywords or for all keywords in your account. Google is fairly clear about their policies; you must understand and respect them.
Quality Score, Your Advantage
Most advertisers should think of quality score as a message from Google telling them how well they're doing in the organization and administration of their AdWords accounts. Scores below six should be rare and generally not tolerated. Allowing your account to continue on for months or years full of low quality scores means you're missing out on a huge number of potential impressions and clicks and consistently paying excessively high per-click prices. Why would you want to do that?
Craig Danuloff is vice president and chief product officer at Celebration, Fla.-based marketing product and service provider Channel Intelligence. He authored "Quality Score in High-Resolution," which was written with technical support from Google. Reach him at firstname.lastname@example.org.