A reader might predict that Tom Walker would make the deal with the devil since the riches would make him "wealthy for life." After all, Tom and his wife are both described as "miserly" which means that they hoard wealth and dislike spending money. It is quite surprising, then, when Tom decides against making the deal but, perhaps, more understandable when we consider that he often quarreled with his wife and cheated her, just for the sake of it.
After Tom decides against the deal, we might predict that his wife, being so "miserly," would try and make a deal with the devil herself and this does indeed happen. What is surprising, however, is that the devil does not make a deal with her and she instead disappears, presumably dragged off by the devil's horse.
Finally, considering the fate of his wife, it is surprising that Tom returns to the devil to sell his soul. The "regret" he feels from his new way of life as a moneylender is, arguably, the biggest shock of all but is effective in conveying Irving's central message: that greed will only lead to self-destruction.