There is no proof of purchase when it comes to karma. As popular as it is, the existence of karma is no more provable than the existence of God. Both of these are massively believed in, weighing in at 90%. This tells me that the belief in God and Karma are not exclusive and that underlying the faith we have is a desire to quell the fears caused by the unknown. Faith and belief are powerful beacons for our guidance and survival, allowing us to create positivity and do good to one another.