I've given lots of rides to people I didn't know well but always have had some kind of connection to them -- friend of a friend, friend of a local pilot, colleague, etc. On the other hand, there's someone I know well who I absolutely will never take for a flight. In the past, he's had suicidal episodes. He's a great guy, really smart and, as far as I know, okay right now. But I'm never taking him flying. I don't have sufficient trust in his mental state to risk it.
Also, I would never, ever accept money from a stranger or acquaintance for taking them for a flight. Never, ever, ever.