We don't usually discount the bikes at our shop because with the warranty tune-up package we offer, we don' t really make that much on the bike. It's the accessories that save us at the end of the day, so if someone wants to barter, we usually do them a favor on the lock, the helmet, the lights, etc.
Keep in mind that my shop mostly sells bikes in the 400-1000 category, with fewer sales in the upper limits. If someone wants a 2500 MTB, then we might work the numbers more.