Some indications can be taken from Some Heuristics for Evaluating the Soundness of the Academic Mainstream in Unfamiliar Fields:
Low Hanging Fruit Heuristic
if a research area has reached a dead end and further progress is impossible except perhaps if some extraordinary path-breaking genius shows the way, or in an area that has never even had a viable and sound approach to begin with, it’s unrealistic to expect that members of the academic establishment will openly admit this situation and decide it’s time for a career change.
Thus: You are likely having imaginary expertise if all low hanging fruits in your field have been taken.
Ideological/venal Interest Heuristic
You should be doubtful about your expertise when
things under discussion are ideologically charged or a matter in which powerful interest groups have a stake.
Note that these concern your expertise despite you actually being an expert.
You should note that these cut both ways - given a field of research, they reduce (ceteris paribus) the trustworthiness of both layperson's independent attempts to form an opinion about this field and the trustwortiness of the established experts in that field.
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