Sticky at the top of the forum has the list of site supporters. Google for "DVC resale" returns over 100,000 hits. Some of these I've heard of, some I haven't, some aren't germane. And there's eBay, too.
They don't have the lowest prices but I've found http://www.dvcresalemarket.com/ to be the most professional and organized. Great website and app as well.
Fidelity typically has the lowest prices but you have to move fast, within minutes of a new listing.
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