1. Deadman still alive. These are easy to spot as they appear dead on the ground but with a life bar full. They may look as though they are there but they aren't. Actually they are running around invisible and undetected. They can't be killed using normal means except only if you are lucky enough to hit them correctly like with a flame thrower, grenade, headshot, etc. Hosts should automatically kick this person out.
2. Shot from a person on a ladder or hanging. Easily detected by someone noticing a person hanging, but not falling after a certain time getting kmills still. You can end it by stunning the visible body or killing it. Players and hosts you can kick this guy right away or even teamkill at disgression. Getting a Tarantula rank for teamkilling cheaters is actually not a problem with me. In fact if you are one of those rare Tarantula ranked guys who got the rank this way. More power to you.
3. Warping and Disappearing. Ever see a guy vanish and then reappear elsewhere? He's probably using a pedal device to temporary stall the game's connection like the one used in Halo 2. Kick this guy right away or report him.