@MOKKA Nah, you're safe. If you were offering the game for free for reviews, or some kind of incentive, THEN it'd be manipulating the system (*cough cough digital homicide cough cough cough*), but simply just saying "hey, look, if you played my game, please leave a review because it not only helps others find and play my game if you liked it, but also helps me have feedback to improve later games, and if nothing else just lets me know people have played it" is fine.