I was at the grocery checkout last week when a group of teen boys were buying dozens of boxes eggs which were on a buy one/get one free with no limit.
I loudly informed the checkout clerk that the store had a legal right to refuse to sell and all I got was a shrug of shoulders, not my problem lady.
Should have told the manager. The checkout people have no authority. I have developed a pleasant relationship with the managers of the grocery stores I shop in and if they know you are a regular customer, they listen to what you say.