Early in "The Cask of Amontillado," Montresor repeats the line, "I have my doubts," to Fortunato. In your opinion why does he do this?

When Fortunato exclaims, "'Amontillado?  A pipe?  Impossible!'" Montresor seems to admit to Fortunato that he also has some doubts about whether or not the pipe of Amontillado he claims to have purchased could be genuine.  Montresor has already told us that Fortunato absolutely prides himself on many things, including his discernment as a connoisseur of wine.  It seems to me that Montresor's pride will not allow him to totally paint himself as the gullible buyer of a product he likewise knows to be impossible.  He claims that he has doubts about the wine's authenticity in order to assuage his disgust at having to play dumb for a man he hates.  Even to pretend to need Fortunato's assistance seems to be distasteful to Montresor, and his repetition of the line, "'I have my doubts,'" indicates his inability to completely defer to Fortunato's judgment, even in service of his plan.