If you order a book or two from Amazon, they know how to pack them. If you order more than that, they just throw everything into a thin cardboard box, and if the books are heavy, they then sometimes throw that box into a mail bag.
Thin cardboard boxes with heavy books inside isn't a very good idea.
Look at all the packing material used. That's like ... four? plastic balloon-ey things. That all burst the moment they were put into the box.
So I should have learned my lesson by now: Never order more than two books at a time from Amazon.
Alternatively, Amazon could learn how to back books into boxes. I think they should know how by now.