Oh wow, I’m sorry the ending got spoiled for you. I just finished reading the series for the first time this past January (and I’m 40!), and I would have been really mad if that had happened to me. They robbed you of the opportunity to experience it for the first time and react to it in the context of the story.
I still see people mention now and then that they’ve never read the series. The store should have at least given a warning if they weren’t creative enough to find a way to advertise the story without spoiling the earlier books.
I'm almost glad that I waited to read them because if I had read them at their intended age I'm not sure I would have understood them. Most of it probably would have gone right over my head. But I was really shocked the store would just blurt out a lot of spoilers about the end of the series. I would think that being a book store they would understand that readers hate being spoiled!
I still see people mention now and then that they’ve never read the series. The store should have at least given a warning if they weren’t creative enough to find a way to advertise the story without spoiling the earlier books.