Henk V.  The author is presenting an opinion on a news site. So he can express whatever opinion he likes. It's a false equivocation comparing it to a medical practitioner (or something similar) who is a qualified professional charging for his/her services. 

Why don't you present a case on the merits of the article on where you do not agree and why? That will be far more valuable than trying to shoot something down based on your perception of what constitutes an expert (which the author does not claim to be).

Even if the author does not hold an economics degree (or whatever standard, in your opinion would suffice) does it necessarily disqualify them from presenting an opinion piece? If that were the case then people like Trevor Manual (and many others including senior political leaders who are by no means 'experts') should not present articles to be published here. I find Trevor Manual's articles fascinating. Yet he is not an economist by training.