I think your chances are slim of finding someone who sold to him/her here on DVXuser. Take a look at the user's feedback rating. It's always a good idea to take a look at previous high-value transactions and note if other seller left positive feedback or not.
Selling is generally pretty safe as they have to send you the money before you ship it.
Just don't answer the private message offers. As long as the sale goes through eBay and Paypal, you're pretty safe.
I had a fake buyer recently (using hacked account), but eBay messaged me that the buyer was fake with a couple hours (and payment was never sent anyway).
I think my major concern is trying to get a refund, sending a broken camera in its place back and running off with the new camera and the money. Or am I being paranoid?
I would be careful... Don't want to alarm you but I just sold my FS-4 in working condition and the guy says it doesn't work. Paypal awarded him a refund if he returns the goods. I recorded the serial number already so I'll be able to make sure it's the same unit, but the guy could have opened it up and harvested some parts or something, I have no idea. I would deal locally with items of that value!