Good news: the poster arrived, and it's genuine.

Bad news is: it's the 22x28 instead of the 36x24 model that was advertised. Even though I got a nice deal on it, I had to leave negative feedback for the Ebay seller. Good thing I didn't order a frame for it straight away.

Still, it's a great poster! There's only the tiniest of marks in the bottom right corner near the edge. I went over it with a 5x loupe to check out the printing and other details, and it's flawlessly sharp. I'm convinced it's the real deal

After it arrived and passed muster, I ordered a frame for it. A nice glass-front model with black aluminium square edges.