Just so you know, Microsoft have made a full post explaining everything on their website. This information is from quite a while ago.
At the moment, they say that Publishers can choose whether they want to charge a used game fee. However, these used games must go through specified retailers before they can be sold on. So, anyone at a small shop won't be able to buy or sell used games.
You can lend games to your friends at their house as long as you are playing on your account. Your friend can come over to your house and play your game on his account as long as it is your Xbox.