How concerned should Buddhists be with the actions of others?

Even as I find peace and contentment in observing the 5 precepts and following along the 8 fold path, I realize I sometimes unintentionally benefit from those who don't live in this manner. For example a friend takes something that wasn't freely given and shares it with me or a nearby person kills the insect flying around that I was trying to ignore. If I have not encouraged people to do such, should I be concerned about their actions or remain concerned only with my own intentions and actions?