I figured I would bring this back up, as it just happened again. Probably 1/2 of the postings disappeared.
This time I looked a bit closer, especially at the "completed listings" section linked off the same page. It appears that all of the ones that disappeared are now there, showing "auction ended as item no longer available", or some such. Looking into it further, items sold by those sellers are the ones that have very weird selling histories that show almost certain shill bidding, which probably explains the purge of them.
One guy has nearly 100% sell percent of both no reserve and reserve auctions (most sellers of class b's don't get 10%), but then the vans show up again in a couple of weeks. He has sold some of his vans 3-4 times, under 2 different lister names. The others were very similar.
I would encourage anyone looking at class b's on ebay, or anything else that is expensive, to check the seller sold item history and see if he has sold the same item repeatedly. If he he has, it is almost certain that he is rigging auctions to try to run up price and not have to sell to a winner at a lower price.
If you see listings that fit the profile of this scam, flag the listing to ebay, as they even have category in the report section for it. It must happen a lot.