I've looked at demos that, i have been told, are the most clear evidence of a walhack in progress and, for the life of me, I can't tell.
Since viewing that clear walhack demo I have decided I cannot tell a walhack if it were staring at me through a wall. So I say little or nothing about hax anymore. I just play.
My point is...I think it takes a certain "eye" to "see" that someone is walhacking, even in a blatant demo. Some have it, some don't.