I'm not doubting that you know your job, but merely trying to understand it from an outsider's perspective.They are not "randomly" stopping people. We are looking for gangbangers and once we identify them we have RS for a terry stop/patdown. Wanding is a more efficient method. We know our jobs even if the news doesn't.
The end result, if I were to get stopped, would be me refusing the search and simply leaving the premises. Simply having a firearm on me (which is what you suspect) isn't illegal and even if you did see it print or knew I had it - I'd provide you my LTCH and be on my way (even if that meant leaving to avoid trespass).
The end result, no matter how you slice it, is me leaving and not spending any money there.
That being said, I look about as far from a 'gang banger' or 'thug' as humanly possible so I doubt I would have issues either way.