An utter lack of scrupulousness defines the three rioters. Every act they undertake is done without much thought, from their quest to defeat death to the two plots to murder one another.
Had the three men been more careful, it is hard to say what might have happened. Considering all three had murder on their minds, one could argue a more thoughtful approach would only have served to delay the inevitable. The two who planned on killing the one who went to fetch wine might have only waited, but they still would have died from the poison.
Now, an overall greater attention to detail might have made them wonder if the friend was planning on killing them as well, so they might not have chosen to take the wine at all. Then they might have killed the man and gotten away with the money. What causes both parties to fail is that neither expects the other to be equally treacherous.