People often ask me about buying used bikes and I usually point them in the direction of the Bike and Roll annual bike sale. Sadly, they usually ignore me. But the two people who have listened to me have been happy with their purchases. That is a small sample size, but it bodes well.
This year's sale is September 8th, 11AM to 4PM at their location at the old Post Office Pavillion. Get there early I hear.