Should I add this guy on Facebook?

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As a general rule of thumb, I only add people who I know personally. He could be genuine, but then again, he could have more malicious intentions (such as Social Engineering). I'd say stick to e-mailing him until YOU feel comfortable adding him on any other medium. Don't feel guilty about your actions, as you've already done something most people wouldn't do, by giving him the option to e-mail you.