Why is it easy to trust/like some people and not others eventhough both seem to have the same character

Perhaps it's intuition..or perhaps although two people may seen to have the same character there are subtle differences in body language and so forth that send a non verbal messages or 'vibes' that this person is genuine or not.
That way it may not be obvious because it's nothing they've done or said different. That being said I can't explain exactly what makes two people 'click' ... I reckon it's when two people's energies are compatible and that's why people talk of having a 'spark'.