I've bought off Craigslist several times. You have to really know what your looking for and know the differing levels of components. Bikepedia is your friend as sometimes 'that bike' is listed by someone who doesn't know anything.

You'll get more bang for your buck, my replacement cost for my bike (owner upgraded the dickens out of it) as outfitted is five times what I paid off CL.

Only frustrating part I found was all the perfect bikes generously outfitted were always too small so it took a while to find the perfect bike, but find it I did. Hit your LBS up for new high quality saddle swap-outs - the saddle is key If your mechanical, sometimes just adjusting and plotting new parts is half the fun (ohhhh I am still soooo OCP).