Is the story Montresor tells Fortunato about the Amontillado believable?

How does Fortunato expect to taste the Amontillado that Montresor claims to have stored in his underground vaults? Both men refer to the cask as a "pipe," which is a huge barrel containing 126 gallons. The wine must have been aged in the wooden barrel. The pipe would be on its side and slightly tilted forward. There would be a spigot at the bottom of the round end of the barrel by which the vintner could draw off a small glass of the wine from time to time in order to test it. This makes it a little suspicious that he would have to bring Fortunato into the catacombs to taste the wine—but Fortunato, drunk and blinded by pride, follows credulously.

Fortunato's drunkenness—and perhaps his cough—prevents him from asking many questions. He is a clever man, but he is not thinking straight. From the time Montresor encounters Fortunato on the street to the time he chains him to the rock wall inside the niche, Fortunato does not ask any of the obvious questions about the price, the seller, or why exactly they're traveling so far underground. Montresor sets the scene for his revenge by instead talking about Masons and his coat of arms.