I wonder if it depends on the book. I have zero experience with that site but when I've ordered from some places, I will notice a huge difference between how fast some things send. I ordered off another place a while ago, I got some children's books as well as a recipe book for myself and another book, they all took different times to ship. I think it's to do with different warehouses.

Though, maybe it is just your mail carrier hating you. 😛