Assuming that Arthur is knowledgeable enough to understand all the technical arguments—otherwise they’re just impressive noises—it seems that Arthur should view David as having a great advantage in plausibility over Ernie, while Barry has at best a minor advantage over Charles.
This is the slippery bit.
People are often fairly bad at deciding whether or not their knowledge is sufficient to completely understand arguments in a technical subject that they are not a professional in. You frequently see this with some opponents of evolution or anthropogenic global climate change, who think they understand slogans such as “water is the biggest greenhouse gas” or “mutation never creates information”, and decide to discount the credentials of the scientists who have studied the subjects for years.
This is the slippery bit.
People are often fairly bad at deciding whether or not their knowledge is sufficient to completely understand arguments in a technical subject that they are not a professional in. You frequently see this with some opponents of evolution or anthropogenic global climate change, who think they understand slogans such as “water is the biggest greenhouse gas” or “mutation never creates information”, and decide to discount the credentials of the scientists who have studied the subjects for years.