Well, my children wouldn’t be acting up for such a prolonged period of time as this one apparently was. And I would either discipline the child myself and if necessary, leave the store.
By the way, spanking is not a beating in spite of what liberal do-gooders have decreed.
Years ago I had a girl friend who had an exceptionally bratty son. He frequently deserved to get his rear spanked hard. But I never laid a hand on him even though he'd punch and kick his mother who never did anything to him. You simply can't touch other people's kids.