Guessing you are referring to this one-
Attack of the Clones Yoda ImaxVery hard to say. It is possible he came into a stack of them as it has happened before for different posters.
On the negative side- He says the poster is smaller than the correct 27"x40" at 26.75". I cannot access mine easily to measure so cannot give you a direct comparison and some times especially on lower price posters dealers and auction houses do not always measure every one they sell so derivations can be missed. His description also uses a lot of the typical "reprint" warning keywords/phrases like "NEW" in capitols. The quantity, has sold over 100, makes it a bit more suspect as well.
On the plus side- He has listed the poster in the "Posters>Originals-United States>2000-Now" category so, speaking from experience, if you take a gamble, get the poster, and on inspection find out it is a repro or bootleg it is a no brainer to get a full refund including shipping through E-Bay. The seller will usually take it back without question, if not the dispute process will go your way on it. He also uses the phrase "This is brand new old stock." which means that it is supposed to be original stock, not a later print from somewhere else but in as new condition also referred to as NOS in the car world among other places.
In the neutral corner- Although the price is a little low $40 with shipping, it is not insanely low.
If I were in the market for one, at $40, I would give it a shot knowing that I could get my money back and would only be out a little bit of time.
Just me 2 cents.