In John Wick 1, an assassin named Perkins decided to take Viggo's contract to kill John at the Continental. As we learned early on, the repercussions of violating the Continental rules are extremely severe, leading to death.
What I don't understand then is why Perkins would not only believe $4 million would be enough to save herself. As Winston says at the end of Chapter 2, he notes that "John's life is now forfeit". So as any reasonable assassin would, just as Cassian and John respect the rules of the Continental, why would Perkins both take the contract and meet Winston? Was she just an amateur at her job?