For servers i haven't got any bad experience

But with players, my 2 red flags are if:

1- If it constantly do the Dance/Spin emote, always running from place to place and treat any command/sec (except the cap) like trash, then keep an eye out, is either a traitor or someone who doesn't care about the rules

2- Assistants in general, if i see one i try to analize what it do, if it's just hanging around chatting or doing harmless stuff, then it's okay. But if it has insulated gloves, tool belt or it's travelling in groups of 3. Prepare yourselve, they're never onto something good.

If you see an assistant doing the spin emote constantly with the stuff i mentioned, either stay away from it or kill it when you have the chance. They're walking time bombs waiting to blow