Buying a bike should be fun. Find 4 bike shops in your area. Take four evenings. Go to each one. Say you want to buy a bike to ride to work. Buy the one you like the best from the store you trust the most. Bike are fun dang it.

If you chose the route of buying used, the LBS is going to be helpful they will charge you for stuff and labor. They will service your bike, but it will cost something. They like selling parts, too, not just bikes.