The situation you described could be an example of the fallacy of appeal to authority, where Doctor Montgomery is using his position as an authority figure in the medical profession to persuade his patients to follow his recommendations, regardless of whether they are necessary or not. By insisting that all his patients visit him for follow-ups every three months and charging exorbitant rates for each visit, he may be exploiting his patients' trust in him and using his authority to benefit himself financially. However, it is also possible that Doctor Montgomery has valid medical reasons for recommending frequent follow-ups, and the charges for his services may be reasonable and appropriate for the level of care he provides. Without more information, it is difficult to determine whether this is an example of a fallacy or a legitimate medical practice.