I bought a pair of used regs off craigslist. The guy made us a deal on 2 bc's, the 2 regs, and even threw in a really nice suitcase/bag that has rollers, etc. made for flying with dive equipment. All this equipment was a few years old but hardly a scratch on any of it, meaning they were only used briefly (which coincided with his story). I couldn't pay for half of the new Titan reg I've been drooling over with what I got all this for. So, I paid $175 for the whole shebang, paid $140 to have both regs serviced right off the bat, have used them for 3 trips and love them (about to take them on a Fiji trip this October).
You can justify it either way, if the deal presents itself better either way. And if the person selling is as honest as this guy was!