A customer is not always right.
So, what business are you in? What can I get for free? Heck, in my mind if you dicked me over I should always get something for free if you want my business again right? What if what you give me isn't enough in my mind? That said, sometimes it is better to give some free stuff out just to shut the butthole up.
The guy at the counter did nothing wrong IMO, and he apologized for it afterwards. Not sure how much blood you want from him, but if I were in that store and he did what the OP said he did, I'd go back because I appreciate the fact that he's looking out for other customers. That said, the OP didn't mention in her original post that she was already addressing the situation with her son, in which case I could see why see was getting burned over it.