Sometimes it is hard to tell. I had a situation where my neighbor poured some left over paint in the back corner of my yard killing my grass there. I was upset, but the Lord's small voice told me "Karl, vengeance is mine. I do that. I take vengeance."
So did He? Well, my neighbor planted grass in his backyard three different times and each time it wound up dying. So while my grass is all fine now, his back yard is dirt.