Over the past few months, I've had several occurences of items not arriving. After contacting Amazon, I was told I needed to contact the vendor to correct the situation. In one instance, the vendor sent out replacement goods. In the other, I did not even receive a response.
I purchase (well, one of my employees does), between $5 & 7,000.00 of consumeables and MRPs, for my manufacturing plant each month, with generally excellent results. The key to safety on Amazon are the words "free returns", along side of the price.
I also believe all retail is cyclical in existence and Amazon will be contending, in years to come with others, such as Walmart (if they ever fully get their E-commerce off the ground).