If it was a fake, it's very closed. I would say it's genuine. Comparing with other ones, there're some details I don't like... but that could be because the pen or the surface among other factors. Just my opinion ;)
Hope you'll be replied by someone with more Mantle's knowledge than me.
It looks likely real to me but the photo is not sharp. It's hard to tell for sure that the autograph is live ink. Get a large, sharp photo before you buy.