Fair is a pretty objective deffinition:
Fair: that which must be done according to (natural) law or reason. This is where the fine line lies between a civilized action in accordance with the Law, or an arbitrary one that subverts the Law to use it at will. A claim about an allegation must be fair, meaning it must be true and accurate. Since it is very easy for the alleged victim to invent a crime and then claim damages, the accused has the right to prove that he committed the crime in question. And if both parties do not agree and the accused does not recognize the damage or fails to reach an agreement, then the intervention of a totally neutral external arbitrator who judges with absolute alienation from Natural Law is necessary.
If I killed your tree, it is fair I provide you with another similar tree. If we disagree on what a "fairly similar tree" is, then a neutral party can intervine, which would decide what a fair substitute is. There is really not much variation on what fairly similar trees are, only possible variables are species, quality of fruits, age, size, etc. All measurable things. If you refuse to acknowledge evident similarities, we can call a judge.
This is all logical and natural. We all have it inside us. And we all know this is good.