Personally speaking, I think the law of karma does not exist. A very direct real life example is that your good deeds do not always being repaid with good deeds. Of course, bad actions certainly will not be responded with good actions.
In another example, if you kill a chicken and the chicken will return to take your life in next life. But the fact according to karma is that it was that the chicken owed you a life that you take its life this life. This is equal and null.
Even Buddhist teachings from various schools contradicting with each other.
In Diamond Sutra it is stated that: