Microsoft introduces self-serve refunds for purchased games on Xbox Live
The mechanism is very simple: just enter your purchase history page from PC of your Microsoft Account, and request a refund where possible. Obviously though you cannot request a refund for purchased games for a long time or you have already played for several hours: the rule is that you have not played for more than two hours (warning: where play multiple accounts are totaled) and that the purchase was made within the last two weeks of the request for reimbursement. If you stick to these terms, you will always get a refund.
This opens the door to a very interesting possibility: you want to buy a game but you're not entirely convinced? Buy it, giocatelo for less than two hours and, if you don't like it, I do pay back immediately. In short, with this system you can get free demos of each title on Games Store, you just have to be careful not to exceed two hours of play! Be careful though not to abuse it, because MS tells us that it could take action against those who exceed in using this feature.