I want to talk about business.
You know how to make money out of a GREAT game like this one? NOT by harrassing the players every five actions with the need to purchase more coins or kreds.
That is the WORST thing you can do, it just drives people mad and make them want to stop playing right away (don't believe me? Read the other comments.). Want to know what works? PUTTING ADVERTISEMENTS ON IT.
I am pretty sure you'd get a much better deal and your game would be rated 4.5+ with that change.
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