If you use their cloud products, ala Netflix, they may decide to compete with you any moment. Netflix may have been too far along to be beat but the next product won’t be. If you sell products on their market place and if they do well you run the risk of them copying you. If you do anything in their ecosystem you are living with the fear that the lion may wake up and swallow you whole at any point and time.
Edit: Maybe I’m a bit paranoid but this feels like a great way for them to get to know exactly who your customers are and what their behavior is. All the while training their own personalization to get much better.
Of course, Amazon could lie, but now if Netflix has a reason to suspect wrongdoing, they could sue.
This isn't how the world works.
And the example of Facebook with Onavo is also not plucked out of thin air.
Sure, it's not how all of the world works but for the big players, it's a important tool in their toolbox.
You are not paranoid. That's exactly the business model of the retail website when hosting independent merchants.
The lion waits until you finished eating dinner...