Even the posting of a sign does not create a criminal offense for open carrying as carrying past signage is only a crime if one is carrying concealed under an otherwise valid concealed carry permit.
Short Version: yes, it is legal to open carry into an ABC store (no matter what is posted or written on the door). However, when you are asked to leave (and they can legally ask that you leave) if you don't, you can be charged with criminal trespass.
If there is a sign banning weapons posted, and you enter, you could easily be charged and convicted with trespassing.
"� 14‑159.13.� Second degree trespass.
(a)������ Offense. � A person commits the offense of second degree trespass if, without authorization, he enters or remains on premises of another:
(1)������ After he has been notified not to enter or remain there by the owner, by a person in charge of the premises, by a lawful occupant, or by another authorized person; or
(2)������ That are posted, in a manner reasonably likely to come to the attention of intruders, with notice not to enter the premises.
(b)������ Classification. � Second degree trespass is a Class 3 misdemeanor. "
I would say knowingly carrying past a weapons ban posted entrance would fall under section (a-2) of this G.S.
You are no longer authorized to enter if you are not following posted signage. I don't think a DA would have a hard time convincing a judge of this. And your sentencing would probably be stiffer than someone violating similar signage regarding no shoes no shirt no service.
So IMO you're giving bad advice here.
Furthermore, I wholeheartedly agree with a business owner's right to select customers. Those who discriminate will be less likely to survive a competitive market.