Read this on Engadget Retailers reportedly briefed on how the Xbox One used-games market will work
As everyone else has already said, blocking used games is an utter howler. I don't care about used games on the PC as the games are normally reasonably priced but not so on the xbox. I know they won't lower the prices as their current online 360 store still tries to sell ancient games for comical prices.
I wonder how long it will be until someone manages to work around the playing offline and second hand games thing anyway. I am hope that the method of checking is something silly that can just be worked out in a request. If so, you will just be able to divert the xboxes network calls to someone else (locally or otherwise) that will return authentication signals back.