There is a publication called Shutterbug that is a great place to buy and sell used camera gear. You can find a copy at Barnes and Noble (or find them online). You can also sell it on ebay, and some camera shops will sell your stuff on consignment. Then there is the possibility that the place where you want to buy your video camera will take a trade-in, but you will most likely get a better return if you sell it yourself.
Over the past 20 years as a professional photographer I have found a couple of retailers that I would suggest to you. I find that both B&H (www.bhphotovideo.com
) and Roberts Distributors (www.robertsimaging.com
) are great at the whole customer service and have fair prices on both still and video equipment. I have found that it is worth paying a dollar or two more if the stores stands behind what they sell.
If I can help any more let me know.