Your link is based on a totally different set of circumstances. Wearing a gun in a store COULD make other customers uncomfortable and since, in your example, it appears the person asking the question is not a protected class, he could be asked to leave.
However, I think the problem with this scenario is the clerk refused him service based on HIS PERSONAL political beliefs, not on store policy which may change the equation. I am not an attorney, but unless there is store policy against waiting on Trump supporters, the guy acted outside the scope of being an “agent” of the owner.
I told you I was charging. $20 to Free Republic for your lesson. Did you read all of the attorney’s answers? Obviously not. Read them again. The simple, conservative principle is that it’s private property. And you can be asked to leave for almost anything unless you are a protected class.
(I don’t practice but I did go to law school. make sure you send your donation)