I've been looking into this as well and my hypothesis is that there are several sites (most of them having time share in them) that scan other sites for their listings and represent those listing as their own so that the site appears to have a lot of listings; I think they also have some of their own listings, potentially the ones you're finding are the lowest priced
I've also read that some of the sites charge the buyer fees above and beyond normal closing costs (hard to say, many of those sites are not transparent on fees) which is potentially how they are generating revenue; one site in particular (forget which one) supposedly pushes buyers to use a specific title company that has a significant markup relative to other title companies that process DVC purchases (it was claimed that title company had some relationship with the site)
personally, I avoid those sites when I compile listings because the lack of transparency around fees, confusing nature of the websites, and the large number of listings that I question; the other ten more DVC focused sites have, at any given moment, 300-400 active listings
you can still pursue any deal you find no matter the site; but if it wasn't on one of the DVC specialty sites, you should ask lots of questions and get costs and fees in writing so you can do a true equivalent comparison