Selling accounts to share games may not be ILLEGAL but it IS against Xbox terms of service which means they can delete your account if you are found to be using this service to play games. It is also unethical, as you take ownership of nothing apart from the login details.
Also you recieve NO ownership of the game, only access to an account which can be revoked at any point and from what I am reading, has been on many occasions
This company and others like it DO NOT give refunds and as a consumer you have NO rights if you give them your money. DO NOT BE CONNED BY THESE PEOPLE, IT IS A SCAM TO TAKE YOUR MONEY