I'm not sure there is a set criteria for unbanning cheaters per se. Here are some questions I ask myself when considering banning/unbanning cheaters.
Was it a glitch or an intentional edit of the mod files to obtain an unfair advantage?
Is there a reasonable doubt?
Is the accused a troublesome member of the community?
Has he admitted to cheating?
Has he apologized and assured us it won't happen again?
How long has the member been banned?
Has he attempted to circumvent his ban at any time?
How severe was the cheating? (First time multiboxers don't generally get banned. People editing system files do.)
Usually, when a player is banned indefinitely, we will not consider reinstatement for at least six months. Depending on the severity of the cheating, this may be longer, particularly if there are issues involving the player that go beyond cheating.
@Wizard. The particular case you refer to, the player was banned for four months, not one month. There was reasonable doubt among the staff that his situation was a glitch, not cheating. As stated in the OP, if there is a reasonable doubt, we will fall on the side of mercy. Even so, this player is under probation, can only post in RP threads and has been warned that if he is involved in any situation like this again, he will be banned indefinitely.
The fact that he was found attacking your base again, may be irritating to you, but it is not cheating. Please know, that it is extremely difficult to judge when someone is cheating or it's just a glitch in a 10 yr old mod. We value those who follow the rules, but we also believe in giving people a second chance, if it's warranted.
Last thought. This thread does not exist to argue the merits of unbanning specific members of the community. It is simply to inform the community of the general thought process of the Admins as they consider banning/unbanning cheaters. Please do not post here arguing with us that so and so should, or should not, have been banned/unbanned.