You can’t compare a restaurant to a grocery. The way business is conducted is very different.
In a restaurant, there is someone providing the food before you pay for it. This is not the case in a grocery.
Obviously, if the store isn’t makpid, it’s okay, but I don’t know how you could just assume that they’re not.
The fact that “it’s done” doesn’t convince me. The store owner nay not want to antagonize his customer by telling them to stop, but that doesn’t mean that he likes it.