Just got back from the local specialized dealer an they have confirmed its not a genuine s-works, they rung specialized and ran the serial number by them and they said its not one of there's and their records go back to 2004. The shop also said its fat too heavy and it looks like its was white originally. So there you have it as I expected a fake!
That's a real bummer mate. Hope you get your cash back from the seller. For what it's worth an easy mistake to make, someone has gone to a hell of a lot of effort to fake this.
I'd say it was way too heavy too, i've had a couple of 18" M4 stumpy frames and they weighed about 1400g so the 1900 of your frame is way heavy as I thought the Sworks stuff was lighter than the more normal stuff. 500g on such a small frame is a lot of extra weight.
Matthew