The Devil plays hard to get in this short story when he enters into negotiations with Tom about the money that he has access to and how he would be willing to give that money to Tom, but only under certain conditions. Note how these are referred to in the text:
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, and he was not a man to stick at trifles where money was in view.
It is quite clear that these "conditions," as the reader can tell from the end of the story, concern his own soul and giving it to the Devil after an allotted time. The fact that Tom Walker takes such a long time to think about whether to enter into this bargain with the Devil or not shows just how important these "conditions" are, because for Tom to hesitate when he has the chance of gaining money indicates very strongly that it is a very important bargain. The Devil plays hard to get therefore when he insists on the exchange of Tom's soul for the wealth that he promises him. Having made sure he has selected a man who is greedy in the extreme, he knows he can push for exactly what he wants: Tom's soul.