Is Dupin reliable in Avi's The Man Who Was Poe, and what shows he is reliable?

In Avi's The Man Who Was Poe, Edgar Allan Poe goes by two identities—his own and the identity of a character from a series of his short stories named Auguste Dupin. In creating Mr. Dupin, author Poe created the very first detective character who relied heavily on the skills of observation and deductive reasoning, just like Sherlock Holmes. In Avi's novel, the author Poe is unreliable because he offers his assistance to Edmund but is really only interested in unraveling Edmund's mystery because he thinks it will make a good story; Poe is not actually interested in rescuing Edmund's sister. When posing as the detective Mr. Dupin, however, Poe is reliable because he doesn't stray from the fictional character he created.

One way in which Poe as Mr. Dupin behaves reliably is by throwing himself into the investigation of the disappearance of Sis. It is Mr. Dupin who realizes that, if Sis could not have left the room through the locked door, then she had to have left from the window. Because Mr. Dupin reaches this conclusion, Edmund finds a pearl button from his sister's shoe in the room in the next building; the button serves as excellent proof that Sis was kidnapped.

Mr. Dupin continues to demonstrate his reliability through his investigation despite Edmund's doubts of his reliability. At one point, Edmund distrusts Mr. Dupin so much that he decides to follow Mr. Dupin, who is supposed to be on his way to Mrs. Whitman's home for a tea party. Edmund is very disappointed when Mr. Dupin stops and enters the First Unitarian Church. While Edmund disappointedly waits for Mr. Dupin to leave the church, hoping he'll continue on to Mrs. Whitman's, the reader remains with Mr. Dupin as he climbs to the church's bell tower. There, he grasps a rope, then pulls the piece of string from his pocket he had found on the floor of the bank's vault and compares the string to the rope to determine, "It was the same substance, hemp" (Chapter 11). Later, when Mr. Dupin explains the mystery to Edmund, Mr. Dupin says his comparison of the string to the rope helped him draw the conclusion that Edmund's sister was stolen to be lowered into the bank vault through the air shaft in order to help the kidnappers steal the gold. Hence, even this scene in the church, despite Edmund's doubts, helps portray Mr. Dupin's reliability.