I'm looking to buy a bike for a 20 mile, round-trip commute. I live in the city so I don't want a mountain bike but rather a touring or road bike. I've been looking and I'm not sure which route to go. I would preferably not like to spend over $250-300 USD.

I've been looking at craigslist and ebay as well as some recreational stores in the area and I'm undecided if I want to buy used or not. The only thing swaying me to buy used is the price difference, but I'm too confused on what is actually good/acceptable for a used bike to be able to adequately price the bike.

So my question what should I be looking for and what should I avoid? Also if anybody here commutes on a bike feel free to discuss anything bike related.