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Google's advice is to type "Google Advertising Professionals" into Google Local business search, but nothing really useful comes up.
The best way to stop people claiming to be qualified when they're not, is to create a Google directory of qualified professionals, otherwise it seems that anyone can claim to be a Google Advertising Professional.
If someone uses the Google Professional logo without a link to the Google 'certificate page', then Joe Public has no way to clarify whether they are legitimate!?