You don't often see inscriptions from Bukowski written in script [...]
But a few things - the longhand writing, the "shit yeah," the manuscript style date, the brand new eBay user - ring false.
Interesting. I'd say genuine, but agree with mjp's points of concern, the 'shit yeah' and the date especially.
That could be a sign that it is fake. (because Buk didn't do that.)
But it could also be a sign, that it is legit. (because a forger wouldn't do that.)