I've cruised that site a few times and I have the same questions. Seems they are really more of a middle man and only interested in odd cars they can advertise and take profit from. Relisting is a rarity, they choose what cars are listed and how they are listed, limited contact with company though email only, seller has no control over listing, etc.....
For buyer, I would say if you are close to the seller or have someone else available and can check out the car, like any other auction, it would be best.
If you are selling, I think there are much better avenues....... but this one is interesting and might work for you.
Internet reviews are mixed, Yelp has some poor reviews.
Last June I thought I would present my R to them for consideration on their site. After a few back and forths with many pictures showing everything they requested there reply was " we have never had an SSR on our site and WE don't think it's suits our profile..Thanks for your interest". That being said i just continued to leave it on site here and occasionally put a sign in the window the odd time I drove it to Cruise night when it was too hot to go in the old corvette. They are West Coast based, really cater to the MB, BMW, Porsche, Ferrari and hi-end exotic crowd. I follow it for Corvette, Chevlle and Camaros but they get lots of muscle and some really great restorations on there. You pay an up front listing fee $99.00 IF they accept your consignment and the seller pays Hammer price plus commissions. Lots of Dealers on here disguised as regular guys. Go to "previous sold" ....tons of nice stuff and decent drive videos too. If anyone has bought from them, I'm curious what the commission charges amounted to.