You can go take a look at it. If it's spotless clean, no gunk in the gears, clean hubs, and NUBS STILL ON THE TIRES, it may only have 20 miles on it. It takes more 100-200 miles to get the "new tire" rubber off a tire. Look at it this way.... you probably won't find a nicer bike for $600. I guess it depends on how badly you want that particular model bike. Craigslist can be hit or miss and it takes time to find a good deal.