In "The Open Window" young Vera controls the story, and as such spins a tall tale, a ghostly tale, that she conveys very convincingly to the susceptible Framton Nuttel. He is easily convinced that the open window is a memorial to the hunting party that went missing in the Bog and, is expected back at any moment by her grief stricken Aunt who cannot accept the deaths of her husband and brother.
If Framton Nuttel were the narrator, he would tell us that he is visiting people he does not know in the country, and with that in mind, he would be a little more skeptical of Vera's story. He would have to consider if the open window was a memorial to the missing men or if it was just an open window. He would measure everything that Vera said with a more rational perspective.
He would also not judge Mrs. Sappleton to be an eccentric nut before having a chance to speak to her. If Nuttel were the narrator, he might consider that the hunting party actually went missing, or he could just ask Mrs. Sappleton outright if her husband and brother were out hunting today.
If Framton was the narrator, his behavior would be viewed as more rational and reasonable. Especially if he was unsure whether Mrs. Sappleton was waiting for the ghosts of her husband and brother or for the live version. He could easily place the responsibility of looking silly on Vera instead of on him.
At the end of the story, Mrs. Sappleton thinks that he is both crazy and rude. He rushes out of the house as if he were on fire, not stopping to look at what he thinks are ghosts.
He would also have the last word in the story, and it would not be Vera's excuse that he was afraid of the dog.
He could portray himself as a victim of a practical joke, a cruel practical joke played by a rude little girl.