I'm embarrassed to say I keep coming back to this thread.
Were I to draw a bright line in the sand on the ethical issue of the original hypothetical:
Is it unethical to resell merch purchased at a show for whatever another is willing to pay for it? Hell no, all things being equal, because concert/band merch is not a necessary staple of life, without which the purchaser will suffer.
Is it unethical for the "flipper/reseller" to swoop in at the beginning of the show, buy up all of the merch, thus denying the rest of the show attendees/FANS from purchasing a cherished memento of their awesome show experience? A qualified yes.
SO - my take on the ethics is that if any fans who attended the show were denied the ability to purchase merch by the Ebay Avenger - then I see them as victims of a slightly unethical act... but that left them more $$ in their pockets for beer, so the karmic balance tips back, just a little bit.