I think the most important thing is to have contact with the seller. You might email some questions? I purchased a Surly off of Ebay a couple of years ago. It was an impulse purchase (of sorts), but a shop was selling it and they listed their phone number. I called them, and they answered all my questions. I had to get a few things re-done (for example, they didn't use the correct splitter on the brakes according to my LBS), but overall it was a great experience. After about $100 (including labor), it was perfect. I love the bike. Funny - I was in a shop that's near me (about 2 hours away, but somewhere I go often), and was talking to the owner about the bike. Turns out, it was his wife's bike (he moved to NC from TX).

CA