In most cases, the primary quality required of an agent was a deep knowledge of the country in which he or she was to operate, and especially its language, if the agent was to pass as a native of the country.
I de fleste tilfælde var den vigtigste kvalifikation et dybtgående kendskab til det land, hvor agenten skulle operere, og især sproget, hvis agenten skulle kunne gå for at være indfødt.