Ideally, this board from someone who has more than a handful of posts. Same would go for dvinfo.net if they have a marketplace. You could also try an escrow service if you go with ebay.
tru dat. go to the selling board here. I've seen and heard (read) nothing but good things from this place. And for the most part you can agree that people whom are on dvx have some what of a dedication to either filmmaking or their dvx, which equals relatively decent equipment. just a thought. Ebay is really a crapshoot. Also, try craigslist in your area you can see it before hand. Ebay is locked into an auction, while forums give you an opportunity to communicate with the seller before hand.
I bought my DVX100 less than a month ago off of ebay.
Got a pretty good deal, I think. Got it for $2000 USD with only 40 hours on it.
Was in mint shape. Not a scratch.
The seller had a very high rating of something in the 3000 with 99.9% positive.
I normally don't buy expensive items like this off ebay, but I was in dire need of a 3CCD and couldn't really afford what I spent.
i bought a new dvx100bp from VSA (Video Services of America) for $3231. brand new, still sealed in it's box... very happy! they are an authorized dealer.
What's nice about the boards is everyone already knows the product, so you can focus on the price and fine details instead of scrolling through endless tech descriptions that you were already well aware of if you did any type or research on the camera. I have had a pleasent experience so far in selling my equip.