I would contact him and tell him that you are 100% sure that this is a forgery, as are the members on the Bukowski.net forum. I only seem to have any luck convincing people of this when I give "credentials". I tell them that I have hundreds of authentic signed books by Bukowski (well.. Not really hundreds!), that I have published him and that I have seen thousands of authentic signatures. Usually at this point, they shut it down.
Think of the poor guy that wants a signed Bukowski book for someone as a gift. I think of my kids getting me something like this as a present. It arrives and it is signed by "corky". Of course, it would be cute that they wanted to get me something like this, but a big part of me would be pissed off for my kids, who just got RIPPED.
No real Buk fan will believe that this is real. Still, It will sell to someone that thinks that it is real.
I would let them know.
Bill