I can understand a small business being uneasy. If I owned a business and saw a person carrying a weapons, even holstered, in my establishment I would be very nervous.
It is a question of liability. In the small town I used to live in a businessman was in the bank depositing the day’s till and accidentally dropped his gun. It went off, shooting him in the leg. The resulting hospital bills bankrupted his business.
After that incident the bank’s policy was no guns in the the bank, period. They didn’t want to be sued if some bystander was injured or killed in a similiar accident.
But if someone walks in with a holstered firearm, I wouldn't be.
Anyone who walks in could be carrying a concealed firearm - in fact, someone who robs a store using a firearm usually initiates in one of two ways: (1) they walk in with a drawn firearm and get right to it (crackhead) or (2) they walk in with a concealed firearm and wait for their opportunity (seasoned stick up artist).
I haven't heard of, or seen any surveillance cam footage of, someone walking into a store with an undrawn, visibly holstered weapon and then proceeding to stick the store up.