It is enough to give a trait of character or a quality to the manipulated one, so that this one tends to validate it then by the acts.
For example, you must have an ecology questionnaire completed. So you go near a garbage can and you expect a passerby to throw something in :
YOU: Ah, congratulations Madam, it has become rare for people who care about the environment like you, and we see that you are concerned about the future of the planet. Exactly, would you have a few minutes to give me to fill this little questionnaire on the ecology?
You have already seen this technique used in conversations around you, even if it was not done for a dishonest purpose. Thus, when before asking a question to someone, we start by saying "Here, you who know you", the person will tend to try to give absolutely an answer, even if she does not know anything about it. Or "You who have the strength" to help with earthworks, etc.