You are right to be cautious and to ask questions early rather than (too?) late.
I could be wrong, but I thought I read somewhere that people driving through a place that forbids weapons, if simply driving through on their way to somewhere else, aren't supposed to be charged if caught carrying because that would violate the person's interstate travel rights... but the firearm might have to be unloaded and secured. I know I'm not quoting exactly, but this might give you something to search up.
As for businesses, it would be nearly impossible for them to know if someone were carrying concealed; and all they can do is ask the person to leave, not place the person under arrest or anything.