Originally Posted by BoldlyDubious
I'm not forgetting that. That's the reason why -in my first posts in this thread- I hypothesized a (short) time limit to request substitution, and the possibility of excluding short-lifespan content from substitution.
If the time limit for exchanging a book is set at (say) 24 hours, only an extremely fast (and dedicated) cheater could defeat the system... and I doubt that he/she will take much pleasure in reading the "stolen" book :-)
But then you need an always on internet connection for your media consumption device and an unbreakable DRM system otherwise you just download it, convert it or copy it to your off line media device, say it's rubbish and return it while keeping a copy to use at your leisure.
It sounds like what you want is a "try before you buy" method (In fact just like the samples found on sites that sell ebooks, mp3's etc), or at the most extreme you want to use Giggles method of have everything you want and only pay for things you want to (i.e. never)