This is a fake, the fraudster behind it keeps trying to sell fake shikishi from various mangaka. He's done a few that he's tried to pass as Miura's. It's truly despicable.
I've edited your thread title to better represent the situation.
No offense man but I doubt any Berserk fan would think that is legitimate Miura art, you can just tell, and even in all of Miuras Shikishi's you can tell it's Miura even when they are quick sketches because of his iconic art style. a lot of the Shikishi's of Guts I've seen are actually really detailed.I'm fine with someone selling something like this but don't put Miuras signature on it.
I saw a couple of other fake shikishi on Y!JA these last few months. What's absolutely maddening is seeing how much these scammers can make from it. Someone shelled out almost $1,000 for one. I'm also so confused...the artwork looks so p*ss-poor compared to Miura's; how can you fall for these?
I think many won't bother to scrutinize. The inventory of shikishi items is nebulous, which makes it ripe for exploitation. I would imagine many will bid out of fear of missing out on a rare Miura-signed piece.