I also use a number of US forums and these guys get talked about a lot, split into two distinct factions 1) these guys are complete rip off merchants and the scum of the earth pushing up prices for everyone or 2) it's a free market, if it works for them well so be it.
There have been a number of clear cases where they have bought cars off eBay, Bring-a-Trailer or Craig'slist then given them a quick polish and a service and put them up for sale at much, much higher prices. You can argue about the ethics of this until the cows come home, if they can find a buyer then, well.. it works for them. From the size of their inventory and the average cost of their cars, they are either laundering drug money or know what they are doing.
My personal dislike for these guys is that they bought the best E30 M3 in New Zealand and took it overseas, so I won't get to see it / stroke it in the flesh ever again. sniff! sniff!