I don't think it's easy to know immediately. I agree with time. I agree with actions speaking louder than words. Don't whisper sweet nothings without backing it up with some consistency in patterns. I agree with reciprocal relationships being a determining factor. I totally agree with the active listening point. It over time displays down the road about being heard and understood-two of my high on the list needs in any relationship. Sometimes a person can be aloof and obtuse but then display knowing your values and likes and dislikes in time through 'action'.
But I think the most important thing is having the wherewithal to be content with yourself to the point if surrounded by but nothing but a pack of thieves, that you can stand still amidst the storm and ride it out until better times.