B&H has a decent used video department. I think with the way the internet has changed things (i.e. ebay, etc...), you'll find most used gear sold personally since there's no cosignment fee when selling in most cases like there is with a reseller.
In my experience, check out reputable forums and their classified sections. Look for people who post fairly regularly and not just to sell stuff. I believe you'll find better taken care of gear this way, IMO.
One thing is since some of these camears can be 8 - 9 years old, you'll wanna see how they've been cared for over the years. Warranty? Cleanings? Plan on a little extra to spend on top of the camera when you get it just to have it professional worked over by Sony or another camera company if you choose another brand.
I've sold a few used cameras (never bought one) and have had really good feedback from those who have purchased. I baby my gear and it's stil possible to find owners who will be selling well cared for stuff, even if it's a few years old. Maybe even more so than looking for a reseller who's being paid a percentage to get rid of it for someone.
And lastly - do they offer a return policy if the camera is not what was promised? Big one to check out.
The classified section of the DVInfo.net forum. You have to be a registered user to see them, though. Also, www.mandy.com has some pretty extensive listings.