The sovereign must have full knowledge of the activities of the five sorts of agents. This knowledge must come from the double agents, and therefore it is mandatory that they be treated with the utmost liberality.
Sun TzuWhen envoys are sent with compliments in their mouths, it is a sign that the enemy wishes for a truce.
Sun TzuIt is essential to seek out enemy agents who have come to conduct espionage against you and to bribe them to serve you. Give them instructions and care for them. Thus doubled agents are recruited and used.
Sun Tzu