I say go with your gut. If someone feels slimy somehow, or the situation feels wrong, by and large something's off somehow. Also, I haven't read the book myself so take this with at least a tablespoon of salt, but I heard that Gavin DeBecker's book The Gift of Fear is a pretty good book on trusting your instincts and identifying danger. It might be good at least for informational purposes. And read up on narcissism/narcissists.

That's my two cents, at any rate.