I would limit yourself to one of the companies who specialize in
DVC. If you look on eBay or similar Internet sites, you're likely to end up with a realtor who knows absolutely nothing about DVC, and that will hurt you. DVC is a rather specialized product, and if the broker doesn't really understand it, you're starting out at a disadvantage.
Of the DVC specialists, The Timeshare Store -- longtime sponsor of these DVC boards -- is clearly the best, IMHO. I have both bought and sold through TTS, and they are great in my book.
I have never dealt with DVC by Resale or Fidelity.
I've only heard good things about Shontelle at DVC by Resale and would certainly have no reservations about dealing with her.
With Fidelity, I've heard some satisfied customer reports, but it seems that every single time a problematic transaction is reported here, it's with Fidelity.
My biggest concern with Fidelity is their apparent complete lack of any due diligence on their listings. The problem with that is that DVC refers all their distressed owners to Fidelity (for $) so their listings tend to be a landfill of troubled contracts.
(Incidentally, for years DVC referred those folks to the Timeshare Store and we never heard about any messed up transactions through them...none.)
Because of the due diligence problems frequently reported with Fidelity -- not their spotty customer service -- I personally would not use them.