Montresor is a rather pathetic figure because he is poor and lives all alone in a huge palazzo. He has no wife or children, although he might have had a family who died. Since he is a poor man, as he tells Fortunato when they are down in the catacombs, he probably has a hard time retaining any staff of servants at all.

"Come," I said, with decision, "we will go back; your health is precious. You are rich, respected, admired, beloved; you are happy, as once I was. You are a man to be missed. For me it is no matter."

When he orders his servants to remain in the palazzo while he is gone overnight, he is not exactly using reverse psychology. Not all servants would behave as Montresor's servants have done. His servants don't respect him because he doesn't pay them enough money. And furthermore, he can't afford to hire the best class of servants. There must be times when he can't pay his staff anything. They stay on because they have a roof over their heads and get something to eat. (They probably also get plenty of wine to drink!) The servants do not "abscond" because Montresor tells them to stay at home; they do so because he tells them he will be gone all night. They don't care if he finds out that they all left to join in the carnival. He can't fire them because he can't get anybody to replace them. And such an enormous old dwelling needs some servants to keep it from ruin. And if he should fire them, they wouldn't have lost anything.

How does Montresor obtain any income at all? Why does he choose to live in an enormous palazzo when he is all alone in the world?

Montresor told his servants that he would not be home, so they should not leave, because he knew they would leave.

Montresor knew that his house would be empty because he made sure that his servants would leave by telling them that he would not be returning home.  His servants don’t respect him.  He is certainly not up to Fortunato’s station in life.  He knows how to get rid of his servants.

I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house.

If you tell people that you won’t be home, so they should not leave—chances are they will leave.  After all, you won’t be there to catch them!  So they all go off and make merry.  It’s carnival season!  Everything is hectic, and most people are just out having a good time.  It is the perfect opportunity to kill someone without raising suspicions.

Montresor chooses carnival time because he knows his servants will leave the house the minute his back is turned and they know he won't be coming back to catch them gone.  It is all part of his brilliant plan to have an alibi in case anyone wonders where he was.  It takes awhile to lure someone into catacombs and bury him in the wall, after all!

Throughout Poe's classic short story "The Cask of Amontillado," the protagonist and narrator, Montresor, explains how he formulated and executed revenge on his unsuspecting enemy, Fortunato. Montresor cleverly waits to approach Fortunato during the hectic carnival season, where he is certain to discover his enemy intoxicated from hours of partying and drinking. After approaching Fortunato in a friendly manner, Montresor plays on Fortunato's pride and affinity for fine wines by telling him that he has acquired a pipe of Amontillado and was seeking Luchresi's expertise to authenticate the wine. Fortunato falls for Montresor's trap and demands that he taste the Amontillado.

Montresor proceeds to guide Fortunato to his palazzo and the two characters leave the carnival together. Montresor informs the reader that he knew his palazzo would be empty because he purposely told his servants that he would not return until the morning. Montresor understands that his servants will surely leave his home and abandon their duties as soon as he departs. This astute observation reveals that Montresor is an expert on human nature and duplicity. Being of the same mind as his servants, Montresor is aware of their true intentions and anticipates that they will abandon their duties as soon as his back is turned. Montresor's plan works and no one is home when he returns to his palazzo with Fortunato. Therefore, there are no witnesses and Montresor can successfully execute his revenge with impunity.

"The Cask of Amontillado" by Edgar Allan Poe is told from the first person point of view of the villain, Montresor. It appears to be written in the form of a confession, with the "you" being addressed perhaps a priest administering last rites. 

Montresor own the palazzo in question and apparently lives alone there except for his servants. He deliberately chose the night of the Carnival for his plot. He tells his servants that he will be gone all night at the Carnival and orders them to stay in the house and look after it, knowing that the desire of the servants to get out and attend the Carnival will cause them to disobey his orders to remain at the house. This is especially clever, because if the servants are called upon to testify in court, they will lie and say they were at the house in order to avoid getting in trouble with their master

How did Montresor know that his house would be empty in "The Cask of Amontillado"?

Montresor knew the house would be empty because he told the servants to be home.

Montresor is an expert in reverse psychology.  He knows that if he tells his servants that he will not be home, but orders them to stay there, they will all take off.  Who wants to be home during carnival when the boss is away?

Montresor is trying to give himself an alibi.  He tells her servants that he would not be home until morning to make sure that they all leave his house. 

There were no attendants at home; they had absconded to make merry in honour of the time. I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.

If they are questioned, they will tell the police that they were at the house all night for fear of losing their jobs.  Thus Montresor is not there, and the servants are not there, but if anyone would ask they will all say that they were there.  No one will know where he actually was.

If Montresor returns with a trowel and the ingredients to make a brick wall, smelling of nitre from the catacombs, no one will be there to see it.  His servants are all out playing while he kills a man.

Montresor is a very clever man, and he plans the murder out to the most minute of details.  There will be no one to see him out with Fortunato, and even if they did they may not recognize him because of the costume.  Also, many people will be drunk.  There will be no one to vouch for the fact that Montresor was not home or describe the condition he was in when he returned.

In Edgar Allan Poe's "The Cask of Amontillado," how did Montresor know that his house would be empty?

In "The Cask of Amontillado," Montressor, the narrator, explains:

There were no attendants at home; they had absconded to make merry in honour of the time.  I had told them that I should not return until the morning and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.

This, of course, assures that there will be no servants in the palazzo when Montressor arrives with Fortunato. It also shows that Montressor employs disobedient servants who have no respect for him.

The fact that Montresor was only concerned about getting rid of the servants that night, in addition to the fact that the palazzo appears to be empty when he and Fortunato arrive, is a subtle way of indicating Montresor's loneliness. He doesn't have to worry about encountering any family members because there are no family members. Any family he may have had at one time would be among the skeletons lining the walls of the catacombs below his palazzo.

When they are underground, Montresor tells his intended victim:

"You are rich, respected, admired, beloved; you are happy as once I was. You are a man to be missed. For me it is no matter."

This may be indicating that Montresor is not rich, is not respected (even by his servants), is not admired, is not beloved. Montresor is not a man to be missed because there is nobody at home to miss him. His large, possibly decaying palazzo is nearly empty.

Why does he keep such a large house and a staff of servants, however disrespectful and unreliable? Venice is a decaying city. The palazzos may be relics of the city's past glory. Montresor indicates that his palazzo is situated at some distance from the city and that the catacombs are under the river--probably the Po River.