It sounds like you are not trusting yourself to recognize what's authentic. Can you tell the difference in yourself when you're being authentic and when you're not? Sure you can, right? If you can trust in your sense of yourself, then you can trust in your sense of others. You'll probably still run into people who do things that seem wrong to you, but trust means you can accept reality and incorporate what happens into a life you love. Which is not to say you won't have to occasionally kick someone to the curb.
Generating your purpose is a whole lot more fun than generating suspicion and distrust.