I do not reply to messages which come from people I do not know or have not seen around regularly on Q&A. There might be an exception where they say something that takes my interest, in which case yes, I will look at their profile first.
They can't even message me
Yes, always, as I would hate to give an inappropriate reply.
Not necessarily, but I do check out their profile before I add them as a friend
gotta be sure its a person haha