Refusing to sell a book on shelve

My mom and I went to the bookstore this morning. She wanted to purchace a book that was on the shelf. When we got to the counter, the lady refused to sell us the book, saying it was on hold for someone else but there was no sign that it was booked on the book. When we pointed it out the lady that it didnt have any reserved sign on it, she became aggresive and rude. We wont be going back ever again