Just for clarification: I did not mean to say that not reading the T&C is an excuse.
But I'd like to point out that, not being able to resell your used ebooks might be forbidden by the T&C but this could very well be against the law.
At least here in Europe the European court of justice decided that software licenses can be resold if you do not longer use them (
Case C‑128/11).
While there is currently no judgement (verdict? decision?) in regards to ebooks, I would bet that the result wouldn't be so much different.