From a FOIA-released WWII training manual for special officers:
Cover
A: General
Freedom – financial – social – movement – leisure.
B: Essential details
Name – history – documents – clothes – behavior (money-associates-tastes-local conditions-table manners-slang-mannerisms).
iv. Coming down to business – change your line of appeal to suit the case, eg for a priest, based on religious grounds, etc.
Let concrete suggestions come from him in the first stages.
Test reactions thoroughly before coming out into the open.
Sound by half-suggestions.
From the first give him the suggestion that we are part of a powerful and well-organized body – prestige counts heavily.
DO NOT TRY TO BUY PEOPLE