An administrator should never conduct himself as if he is "above" the community. You are part of the community and, indeed, have the most responsibility to its members. You should adhere to the same guidelines as the moderators do when it comes to taking control of a disruptive situation. Beyond that, you have the power to permanently ban users but also the power to adjudicate disputes.
New spam accounts should be permanently banned. Bans for established users can be for one day, one week, three months, or one year. Permanent bans of established users and IP bans should be avoided as much as is reasonably possible. If a user comes back after a year ban and resumes his disruptive behavior, he may be banned permanently.
All bans, without exception, must be reported in the "Penalty Box" thread in the moderator board.