In my case, I have a shared computer and one other person uses it. However, I have 2 facebook accounts myself and sometimes I do log in here via facebook when I am already logged in there. (That sounds confusing, but I hope you understand what I am saying.)

But I do not recall ever having conversations here with myself in order to mislead others. And if you look at the post counts, you'll note that the vast, VAST majority of my posts here are from my agoracom account (balducci). I've never intentionally used multiple accounts to get people to believe that there are multiple people sharing the same point of view.