(12C/11C) Changing the firmware

[Dave Britten]

Without better evidence, I would opt for Hanlon's razor here and presume that someone attempted (successfully!) to build one working calculator out of a pair of non-working ones, and the seller simply wasn't aware this had happened. That said, unless the item was explicitly sold "as is, without warranty of merchantability etc.", then the seller should process a return and refund for an item that is not as advertised.