Welcome.
I have never bought from this seller because he is soooooooooooooooo overpriced. May I ask what you spent on this poster? Any reason why you bought it backed? The reason I ask is that i can easily be found unbacked, so maybe it's a preference of yours, which is fine.
It's a great poster and the seller is, I believe, legit (someone else can chime in), just a little crazy with prices.
T