Open carry has been argued a lot on this forum but I still hold the opinion that it does two things:
1) gives the Left a poster child of irresponsible gun ownership, i.e., who but a nut would openly carry a firearm in a store. Despite all the publicity about shootings, MOST people have never been witness of a mass shooting, or any shooting at all, and would consider carrying a gun in public foolish and/or irresponsible. Some businesses are so hysterical that even a uniformed police officer on duty and stopping by for lunch or shopping is refused entry because they are armed. But, those folks may just hate cops.
2) OC makes you a target of thugs who would hit you in the head from behind when you least expect it and steal your weapon while you lay on the ground unconscious. THAT is the #1 reason why I could never OC.
IOW, is he carrying or not? Keep'm guessing or never suspecting.