This is a fascinating concept:
ReDigi opened last year with a novel, if controversial, business concept: let consumers resell their old digital music files. Relying on the “first sale doctrine” — the legal concept that someone who buys a copyrighted item like a book or CD has the right to sell it or give it away — ReDigi operates a marketplace in which fans can upload unwanted songs and buy others at a discount.
Obviously they’re now being sued (on the grounds that they are not actually selling the original, but rather making a copy), but the broader question on whether you can have a used digital good is very interesting. Does the ability to instantly copy something kill the idea of used? What about something that’s 3D printed?