Dissonance theory would say that we are more likely to like them by making an enemy do us a favor. This is because one has to justify internally that they like the person enough to do a favor for them. It means they have to think of you in a positive way as they have done something nice for you. On the other hand, dissonance theorist would say we will not like you in exchange after treating our friends badly. You've got to do bad deed by treating others poorly. One will justify reasoning because they might think that the individual deserved or did not fit anyway. They're not going to claim blame instead the individual deserved it.
