My first road bike (as an adult) was a Bianchi I purchased on eBay. I loved that bike! It was too big for me, granted. I swapped out the stem, lowered the seat, and rode it anyway. That bike lasted me almost ten years before I finally spent money on a new bike.

As long as the price is fair and the bike is in good condition, you can't go wrong. Sizing is important, of course. It probably won't be perfect but then again my semi-expensive "new" bike isn't perfect either.

Check out the seller's feedback, see if this is a business or if he/she is just getting rid of stuff. I asked my seller questions and found that he was an honest enough guy, he just had this bike he never rode. I was really lucky in that he lived about an hour away so I could go pick up the bike when I won the auction