Bests & Worsts Reviews from Amazon

A while after reading my email I was in the Amazon Appstore on my Kindle Fire. Looking at an app I figured "why not, I have those 500 free coins to use" so I clicked to buy and it never even asked how to pay it was just purchasing then downloading. Later I come on here and find out it charged my card instead of using coins. What? So Amazon gives coins to use with my Kindle Fire and then I can't use them from my Kindle Fire? Brilliant move. This whole system seems dumb, why not just have coins be used like a promotional credit? Would that make too much sense? I have 250 coins and the app is $3, use my coins then charge the fifty cents. This is the type of thing that should have immediately been caught and resolved in some sort of beta program, but I guess they gave us coins because we are the guinea pigs.