A thinly veiled rant
Some of the best advice I've ever heard was ostensibly to women about dating, but applies equally to everybody and all their relationships.
If you want to know how a person will treat you once he gets to know you, look at how he treats other people. If you want to know how someone talks about you behind your back, look at how he talks to you about other people.
It's really as simple as that, in life or in business. Don't ignore the signs. Sometimes understanding people is so easy that you can't believe what's obviously true is true.