Tell the victim what? "A stranger offered me money to play this prank on you." The shill knows nothing beyond that. Meanwhile your trained agents need to be a r

Tell the victim what? "A stranger offered me money to play this prank on you." The shill knows nothing beyond that. Meanwhile your trained agents need to be a rare combination of loyal, controllable at home (via families etc held hostage), and yet still worldly enough to function as assassins! That person knows things, and that is the person you want as little exposed (or tempted to defect) as possible.