If you lose they cheated - if you win they never
Hard to say what to watch out for:
If someone raises and someone else
always folds
More people stay in the hand with you than they do others
Hand signals / gestures / words repeated over the game with same result... i.e. someone coughs someone else folds etc etc..
It's hard to say really mate - if in doubt just don't play the game - sure you could find another more legit one about somewhere.