You are unlikely to be liable to professional services surcharge. The Cronin High Court case your refer to there gives you your answer. This case was concerned with requiring professional qualifications in order to practice and be liable to the surcharge. My view is that you are safe enough. The question I would ask is - do you need professional qualifications to sell advertising in an online capacity? You may well have such qualifications but are they needed to perform your work? If not you are fine.