Google has made it very easy to verify whether a Google Partner has really passed all the necessary tests. They have made it possible to create a link that shows all the tests that an individual has passed, the date they took the most recent tests, and the date that their current certification will expire. You can see my tests/certifications from Google right here.
Will Marlow wears several hats, but one of them is that of professional AdWords and Bing PPC manager. He is certified by Google in AdWords and Google Analytics, and by Microsoft as a Bing Ad Accredited Professional.