This post is more than 2 years old.
So, here's a scary incident. I logged into Amazon to access my Cloud Music library (big fan of the service) and noticed it was empty. I checked my profile and noticed that my past orders were also empty. Even more scary, I had somehow lost Prime membership. I saw this for the first time a few weeks back but never figured out how I fixed it. Not knowing what to do, I contacted Amazon via their email support, and, kudos to them, got a response in less than five minutes. But the response... oh my god:
I'm sorry to hear about the trouble you had accessing your accounts. After some research, I've confirmed that you have four (4) Amazon.com accounts with the same e-mail address and different passwords.
This can happen if you've visited Amazon.com in the past and mistakenly indicated that you're a new customer when signing in. A new account with the same e-mail address and a different password would be created.
So just to be clear: Amazon lets you register the same email with another password. For the life of me I cannot imagine in what universe allowing this makes sense. Perhaps they want to make it as easy as possible for users to buy stuff, but it seems like this would bite people in the ass later on - as it did me.