Who decides who is an expert and who isn't?
Well, it's generally considered that an expert is anyone who has studied a topic in depth for years (like university academics in law, economics etc., at professorial level), or who has many years experience in doing the thing they're talking about (like trade agreement negotiators and diplomats), or who have been running businesses or represent the collective voice of 'business (like the CBI, the NUF, the Civil Aviation Authority), or Port authorities, border control personnel, and others who have years of study/experience in topics we might not even have thought of as being associated with Brexit problems.
Also, there are people like the Norths, staunch Leavers for decades, who absolutely see the problems with the current 'negotiations' and direction of travel and who are completely aghast at how badly it is likely to be; based on their studies over the years.
On the other hand, we have our very own Gransnet expert, Petra who is ace at seeing solutions and perhaps could give us her own solutions to the problems of, say, how to solve the Northern Ireland border question without violating the Good Friday Agreement and plunging NI back into civil war...