Purple Cow's Talent audition was held for a whole week. If Silvana truly wanted to find talented individuals to take their souls, she would stay around for a bit longer. Her existence wasn't discovered yet. Only Tom, the one she thought of as the Devil King, knew about it.
Devils were cunning and sly. But at the same time, they were also prideful of their strength and intel. They didn't bother to hide or be discreet like normal humans did. They just attacked and ate souls, reveling in their power and might.
If the Association knew about them, they would laugh at the first man they faced. If the enemy was too strong, they would hide without leaving a trace.
So, how did the Association deal with Devils? They usually put on bait. Weaker ones were sent to lure the enemy out of their hiding while the others ambushed them from behind. This method was used many times in the past.
And now, Tom was the bait.