Another fine example on how NOT to implement IAPs – Da Vinci Pinball Review

You need coins to play the table. You need real cash to buy said coins. The table isn't real, Gameprom (hint: it's a video game). Charge a price upfront for your product, instead of using weird IAPschemes. Full of ads that redirects you out of the game.
Review by ChrisE1G on Da Vinci Pinball.