I'm SUCH a moron. I just typed all of that out, and NOW realize you weren't asking that question at ALL I'll leave it though, since, personally, I think it's decent advice anyways.

What I now realize you were asking is how do you know if some guy is off 2 miles away flying in his own backyard, just waiting to shoot you down.

To that one, I think the answer is probably 'You don't. Hope for the best'

Sorry about the (now pointless) tirade up there.