I'm careful about the content I put on Facebook, so I don't ever have anything there that I don't mind anyone seeing. However, I don't think there's anything wrong with refusing requests from people you don't know at all. I got one a while back from a girl who asked if I was someone she had met in India. I've never been to India, so I sent her a message saying sorry, you've got the wrong person. DH has friends he doesn't know, but who share his last name. I don't think that's the greatest idea. They're probably perfectly normal people, but why risk it?