The Exam is probably for people to get credibility. We have a marketing MSc, Simona, who passed the exam, and that does add credibility when you offer the service - but lets be honest, it just scrapes the surface.
Until you have actually being doing this stuff for a few years, and got the experience of "failing", then and only then will you start becoming an expert - until we focused and had at least 10 customers running together, were we able to really start doing it right.
By doing it right - I mean saving clients money on adwords, getting a higher CTR and most importantly - getting conversions - because without conversions you get nothing, nada - its all just vanity otherwise.
So what differentiates one guy from an other - lets face it the guys at Redfly are great and so are many others. And I am not going to post a link to our service here, because that would be too blatant

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Peter