I'll go out on a creaky limb and say it's over priced. If it's in mint condition and ridden once or twice it's worth only about $575 tops. Also being that it is carbon fiber you take the risk of buying a bike that may have a damaged frame that isn't obvious from appearance, thus I would recommend that you take the bike to a shop that specializes in looking for frames that are damaged or not. If the owner has no problem with you getting the bike looked at and you decide to buy it I would offer $475 if it's in excellent condition but not mint.
There's way too much information in the OP for me to climb the tree, let alone go out on a limb.
Being a 2009, at the newest, with a $1740 MSRP this carbon wonder is yesterday's news. Time has marched on and technology has improved. Seeing that 2009 was the last Blue Book value listed, even that mint, almost no-miles example would be worth around $600 on my Craigslist, I'm in agreement with Froze. An average example of this model would be under $500.
So I think between the two of us, Campybob and myself, I think we have a pretty good idea where your offer should be if you decide you want this bike. If the bike is in mint and ridden once or twice, I would offer $575 and let him counter to no more than $600 with the condition prior to exchange of cash that you, with him to go along so he knows his bike is safe, take the bike to a bike shop that you prior called to find out if they have the expertise to check a carbon bike for hidden damage. Obviously if the bike is less than mint and lets say good condition then bid for less at around $450 and go no higher than $475 with the condition.
It may be older technology like CampyBob said but that doesn't mean it's not any good to ride, it just means that due to the older technology depreciation hit's the value harder.