Amazon itself has been hit or miss in my experience. They are bad for saying something is in stock, then telling me there will be a long shipping delay once I place my order, telling me it is out of stock! One time I bought a book through them and it was back ordered three times at a month each, before I finally gave up and bought it off of E-Bay.
Buying through the "other sellers" listing the item (the affiliates program) usually gets me the same item for less money, especially buying a book used over new, and almost never a problem.