In an interview with Phil Harrison, corporate vice president at Microsoft, he detailed how game ownership will work with the Xbox One, but would not reveal their trade-in plans. In a report from MCV (The Market for Computer & Video Games), their retail sources confirmed that both game publishers and Microsoft will receive a percentage of every used game sale.
The process for trading in games, according to MCV's sources, will happen as follows.
Game owners can only trade in their used software at retailers who previously agreed to Microsoft's terms and conditions. This must also includes integrating "Microsoft's cloud-based Azure pre-owned system into its own."
Once the owner trades in their game, it wipes from their account thanks to the required internet connection to Microsoft servers. Retailers can then take the used software and sell it at any price they desire as long as both the game's publisher and Microsoft see a percentage of the sale.
Now while this system doesn't seem drastically different from the previous trade in system, because retailers like GameStop will see the profit margins decrease, then the value of games will also drop. So if you normally trade in your old copy of Call of Duty to reduce the cost of acquiring the new one, you may only receive half of what you would normally acquire in store credit.
Until Microsoft's comes out and confirms the actual process, this report seems the most reasonable thus far.
Source: MCV