Tom wants the treasure, and he will agree to almost everything.  The one thing that the stranger, the devil, absolutely insists on is that the money from the treasure be used for service to him (the devil)  He proposes to Tom that Tom outfit a slave ship and deal in the slave industry.  Tom absolutely refuses. 

".....the devil himself could not tempt him to turn slave dealer." ( paragraph 37)

The devil backs off this idea and proposes that Tom should become a lender of money.  He would charge high interest to those who could not afford it and foreclose on their property. The devil suggests two cents a month interest, but Tom thinks he can get four cents a month. The devil tells him,

"You shall extort bonds, foreclose mortgages, drive the merchant to bankruptcy." (paragraph 44)

For this he would receive the devil's treasure, but only under certain conditions.  Washington Irving never tells the reader what those conditions are, but he does say that they are serious enough that Tom Walker had to think about them.

"What these conditions were, may easily be surmised, though Tom never disclosed them publicly.  They must have been very hard, for he required time to think of them."  (paragraph 22)

However, it is strongly foreshadowed (hinted) that he sold his soul to the devil, and his place for eternity would be someplace dark, sooty, and uncomfortable.

In "The Devil and Tom Walker," what are the Devil and Tom's bargains and responses?

They set their terms as follows: When the Devil and Tom Walker first meet in "The Devil and Tom Walker" by Washington Irving, Tom is hesitant to make a deal with him because he is unsure if the man he meets is really the Devil and whether the man is capable of doing everything he claims. Tom's wife becomes very upset when she learns of Tom's hesitation to make the deal, and sets out to find the Devil and make a deal herself. She does not successfully make a deal with the Devil, though, and ends up disappearing. After his wife's disappearance, Tom decides to make a deal with Devil.

Although the Devil does not initially seem very interested in making a deal with Tom, they eventually reach an agreement. Irving never explicitly says Tom sells his soul to the Devil as part of their agreement, instead saying it "was one condition which need not be mentioned, being generally understood in all cases where the devil grants favors." 

The Devil insists on a couple other terms in his deal with Tom, too. He wants the work Tom does to make his money to be his work, meaning Tom will be literally doing the Devil's work. At first, the Devil tries to get Tom to agree to be a slave dealer, but Tom refuses. He then suggests that Tom be a usurer, which Tom excitedly agrees to do. They set the following terms:

"You shall lend money at two per cent a month."

"Egad, I'll charge four!" replied Tom Walker.

"You shall extort bonds, foreclose mortgages, drive the merchant to bankruptcy— "

"I'll drive him to the devil," cried Tom Walker, eagerly.