Honestly, price is too much. I bought a 2005 5.9 SL on sale for $3000 back in 2006. (same frame, but with Dura-Ace); and it was from my LBS. Love the bike, was worth more than I paid.
But $2100 for a 6-year-old bike with *6600* Ultegra? I'd look elsewhere, unless you get them to throw in some $200+ pedals and a new Giro helmet. You can find better deals. I think that bike should be priced in the $1600 range *at most* - not because it isn't necessarily "worth" $2100 - it should be cheaper based on what else is out there right now that isn't 6 years old.
In short, look elsewhere. You don't want a 10-year-old bike in 4 years.