What is circular reasoning?
the act of providing evidence to support a claim
the act of supporting a claim by assuming that it is true
the act of arguing that a claim is right because everyone agrees
the act of using a desire to be included to argue for a claim

Where is the excerpt? it’s not attached

The answer is "he was bad enough in all conscience, but the devil himself could not temp him to turn slave-trader. satirical is a synonym for sarcastic. so when the author says that tom walker could not be tempted by the devil he does not literally mean "the devil" but he means that he is too morally upright to become a slave-trader.