Seeing as no one else has jumped on this one yet, I’ll take the bait…
Buying used carbon is considered a bad idea by some people. Unless you have a very good eye and know exactly what to look for, what looks like a perfect bike may have a very serious structural issue. An crack that may be essentially invisible to the naked eye could make the bike outright dangerous to ride. A bike with very low miles may still be a bike that was accidentally dropped or knocked over. Unless you are the origianl owner, only you will know for sure. That being said, new bikes instantly lose their “showroom value” when they roll out the door of the store, and there is value to be found in buying used.
If I could afford a P2C, I would be buying new. If it were an aluminum bike you were talking about, I would be all over craigslist/ebay and scoop it up there.
I saw your other post looking for one for sale. I assume you have been to a good shop and been fitted and know what size frame you are looking for, and more importantly that you are comfortable on that bike’s geometry? There are a few pretty nice bikes in that price range (the new Felt B16 for instance), so don’t buy just based on cosmetics or hearsay.