One way that google explicitly enables these types of scams is by allowing advertisers to display a fake url in the ad footer. Ostensibly this is so advertisers can link to an intermediary 3rd-party tracking url instead of the target page without scaring the customers, but this is precisely what allows scammers to display usps.com in the link to a fraud site. Google even uses javascript to display the fake url in the browser tooltip when you hover over the link!