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.
Washington Irving's "The Devil and Tom Walker" tells the story of Tom Walker selling his soul to the Devil in order to be wealthy. Unfortunately for Tom, his demise came with his own denouncing of the Devil.
Making predictions about a text depends upon a reader's prior knowledge regarding the adage of selling one's soul to the Devil and a tumultuous relationship between a husband and a wife. If a reader is familiar with the tale of what happens when one sells his or her to the Devil, the reader can predict that Tom's life will end in order to make good on his contract. As for Tom's wife, one could predict that he is willing to give her up for anything (since she beats him and steals from him).
When defining if something shocks a reader, one must consider the reader's likes and dislikes. If a reader is one who enjoys horror and suspense, he or she may not be surprised by anything that happens in the text. On the other hand, some readers may be surprised that Tom refuses the Devil's initial bargain (to be a slave trader). Given his temperament, Tom may not seem to be one who would care about human life.
Essentially, each individual reader may react differently regarding his or her predictions and the events within the story which may surprise him or her.