a developer who decided to try out Amazon's App Store, only to be disappointed with the experience:

"Amazon's biggest feature by far, has been their Free App Of The Day promotion. Publicly their terms say that they pay developers 20% of the asking price of an app, even when they give it away free. To both consumers and naive developers alike, this seems like a big chance to make something rare in the Android world: real money. But here's the dirty secret Amazon don't want you to know, they don't pay developers a single cent. ... Amazon is being predatory here, and asking developers (who are often desperate for exposure) to give away their app, in order to promote Amazon. In the end we agreed that we had entered the world of Android development as an experiment, and it would seem silly not to add more data to the experiment we were conducting. The day of our promotion came: ... Amazon gave away 101,491 copies of our app! At this point, we had a few seconds of excitement as well; had we mis-read the email and really earned $54,800 in one day? We would have done if our public agreement was in place, but we can now confirm that thanks to Amazon's secret back-door deals, we made $0 on that day. That's right, over 100,000 apps given away, $0 made."
https://shiftyjelly.wordpress.com/2011/08/02/amazon-app-store-rotten-to-the-core/