How does repbot know whether a user is a bot?
A boolean field in the user DB.
I recently found myself playing kleine_hexe, a bot not identified as such by repbot.
See diane's explaination, it's a "borderline" bot, nevertheless flagged it as a bot today. This has one consequence: bot vouchers/complaints are not counted for reputation calculation.
Do you keep track of them by hand or is do you read the something from FIBS itself?
By hand. Patti must have a similar list for the bot-dropper punishment script, but that isn't shared.