This is a careful art that comes with time depending on the situation and purpose. You never know who people truly are until it shows, but practical observation, test, and fate tends to reveal all that. All you have to do is wait. In matters of employ, friendship, or love I prescribe dealing with a person you actually like despite the flaws or obstacles. The problem with selecting the best textbook example is that the relationship might lack that feel-good substance, making it better suited for contact-less corporate activities, as you would treat a Stranger. Now what you want is passion, excitement, struggle, commitment, sacrifice, . . . all that good stuff. And when choosing such a person, your instincts, heart, soul or what you want to call it, tends to make that choice for you, and all that is required is YOU trusting it.