I think everyone has a BS detector, but not everyone utilizes theirs, or ignores its warnings.
I find that mine seems very sensitive and unless I "feel" sincerity from the person I am sizing up, my BS detector has various levels of "alert" mode.
In "Yellow Alert" mode, I tend to be very guarded with personal information until the individual's behaviour identifies whether I should maintain that status quo or not. This seems to be my default setting, I think, because I tend to use it with all new people I encounter.
In "Orange Alert" mode, there's something about the person that just is not meshing with me. They may be trying to cross a boundary that I do not want them to cross, like bestowing a nickname on me without asking me if I'm ok with it first. That's a signal to me that this person would expect me to allow them to cross other boundaries. FWIW, I was right about my "Orange Alert" regarding the person in this thread.
In "Red Alert" mode, it's clear to me that this person is trying to put one over on me. I know they are attempting to manipulate me by twisting information to suit their agenda. Their actions and sincerity appear to be very contrived and for show. I used to ignore these kinds of warnings from my subconscious. I believed other people who said I was being overly suspicious, when in reality, they were the very people who were attempting to take advantage of me for their own purposes. So now I listen to that little voice when it speaks up, because it is right far more often than it is wrong.