Search for names that contains little to no vowels in it. Most bots have names like hghfodasdh, since there are more non vowels in the keyboard.
Also search for big amounts of time spent in few maps, without doing quests or completing other maps.
Finally detect constant movement / action, since most players will at some point stop moving to think about their build, look at looted items, go to the bathroom, etc, while bots constantly move/attack.
Autoban players that match any of theses rules.
Profit.