I bought a Honda Accord tourer a few years ago, from Deutsche Marques on ebay.
They ran a similar operation, selling cars mainly sourced from auction, at a small profit - they were happy to show the BCA paperwork for my Honda, which showed a £150 profit.
There was no obligation to accept the car, only to turn up if you made best bid, when you were free to give the vehicle any trial or inspection, and reject it with no hard feelings if not happy.
Try that at a car auction, and you'd be out the door fairly sharpish.
So I'd say that these outfits are ok if you go in with eyes wide open, and know your cars.
The problem comes when the unwary treat them like a main dealer, rather than a trade outlet.