It's a rather new frame to have 6 k miles on it, that seems odd.

I couldn't tell you much beyond that. I'm pleased with my CADD three frame, and it's got a good stretch of miles on it. No where near 6 k though. There is one older cannondale frame that I see often, and he rides about 20 a day.

But, YMMV. As with anything used, you take your chances. I would have it taken to a shop and looked over.