In Coup if you claim to be an assassin and try to assassinate someone. If they claim to be a Contessa and you believe them you lose you three coins to the bank correct?
I had this argument with my friend, but to me it just makes sense it would be the same as if you try to take foreign aid and someone claims to be a Duke and blocks you. You can call them out and then if they were lying your action would go through. But if you don't the action is blocked so in this case the assassin would lose their coins and no one would be assassinated.