I've bought and sold with The Timeshare Store -- longtime sponsor of the DIS DVC boards -- a total of five transactions. Every detail of every transaction was handled perfectly.
Also if you check the listing prices between the various websites, you may see that TTS prices are a bit higher than some other sites. Fidelity, in particular, tends to be bargain-basement because Disney refers owners of "distressed" contracts to them. That may be fine if you are a buyer looking for a low-ball price -- but, as a seller, you are probably much better off with TTS.