Gun stores don't want you to carry because people can be stupid and waive loaded guns around. Remember, some older guy shot his own finger off at NCPD pistol licensing. That's why we're all treated to three inches of plexiglass now.
A LGS owner was asking me what I would of done. His customer picked up a pistol and was showing his pistol to someone he knew in a parking lot. An plainclothes officer seen him with the pistol. His license was Target only.
Not knowing the complete details, if I seen someone waving a gun. I would call for a uniform marked unit response.
The 24 hour range was the common answer given when I stopped someone and learned of a firearm being carried.
For safety and liability a gun shop would prefer it's customer unarmed.