By observing and listening.

They are very attuned to your verbal and non-verbal communication. They use covert emotional manipulation tactics for example ‘charm’ and 'flattery’ to get you to like them and desire and value their opinions and validation. they use 'premature disclosure' which is where they share very personal stories (lies) inviting you to feel special and that you should reciprocate by sharing personal things yourself. This will build trust inordinately quickly and give the appearance of a level of intimacy that is not there. Physical intimacy and flirting will also get heavy quickly for the same reason. They may use the 'pity play’ and tell stores to garner your sympathy and make you want to help or protect them. 
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