If your budget is $600 go to performance bike and get yourself a brand new 2013 Fuji Sportif for $499. I think newbies really need to understand that craigslist is HORRIBLE if you don't know anything about bikes. SOMETIMES you get a good deal, but it's usually on higher end bikes where some rich dude watched the TDF and decided to go out and buy a $10,000 bike, just to realize after one ride that it's "hard" and gives up. Then he puts it up for sale for $5000 because he could care less that he's taking a hit. More often than not, you'll find guys who are selling 15 yr old POS bikes, "that could use a good cleaning" for $300 and some poor schmuck doesn't know better thinking it's a good deal and buys it.