You can get pwn’d if the person offering you the bets knows more than you. The only defense is to, when you’re uncertain, have bets such that you will not take X or you will not take -X. This can be conceptualized as saying “I don’t know”
Another defense is updating on the information that this person who knows more than you is offering this bet before you decide if you will accept it.
Another defense is updating on the information that this person who knows more than you is offering this bet before you decide if you will accept it.