Dr. Robinson spends a significant amount of time listening to the king, in the role of Harvey Wilks, addressing the crowd of townspeople gathered to support the Wilks sisters in their loss and to observe Peter's brothers from England. As a result, the doctor is able to present specific observations in his list of comments about the frauds.
He starts with the speech patterns of the king. "You talk like and Englishman-don't you? It's the worse imitation I ever heard." Dr. Robinson continues by arguing that "any man that pretended to be an Englishman and couldn't imitate the lingo no better than what he did was a fraud and a liar."
He points out that the names and descriptions of events cited by the king could have been learned in any number of places, making his supposed knowledge of them meaningless as proof of his identity. Dr. Robinson states that the king has succeeded in fooling the townspeople and that their opinion is swaying the impression of the girls.
He is the thinnest kind of an impostor-has come here with a lot of empty names and facts which he has picked up somewheres, and you take them for proofs, and are helped to fool yourselves by these foolish friends here, who ought to know better.
In the end, however, the girls side with the king and duke, and Dr. Robinson is left unable to do anything more than predict that "a time's coming when you're going to feel sick whenever you think of this day."