Let's say it has to be the death of someone above the age of 30. They have to either volunteer or be a murderer. Since we're dealing with hypotheticals there is no way one could fake having a volunteer or murderer. Otherwise the ritual would not work.
The power received would be key knowledge that only the opposite side(s) have, given to those who perform the sacrifice.
There is no way of knowing what the information will be, only that it is very useful to them.
Would you be willing to use this weapon?
No, I clearly said there was no way of faking having a murderer. You seemed to need further explanation.
I think if someone kills another person in cold blood then they give up their rights just as they forced another to. Thsts why I included them as a sacrifice. The murderer holds no side other than their own yet they are still a life.