Call me a "great big old cynic", but I think your friend may be dissapointed with the results, although I must stress that I don't know this firm and may be doing it a dis-service.
Similar agencies claim to have buyers ready and waiting for a car just like the one being sold. If so, why don't those people buy the car from the seller rather than go through a broker?
If I take my seller head off and put my buyer head on - Worzel Gummidge style - when I'm looking for a car to buy I look in the Autotrader, Exchange & Mart, eBay, etc, I don't go to a broker or agency. The exact same places that agencies find the contact details of people selling cars.
So putting my seller head back on, why would I think other people would go to an agency instead of the sources mentioned above? I think most people would see through it at that point, but I'm sure that after having spent lots of time and money on advertising a car without a sale, those desparate to sell might see a glimmer of hope.
Stick to the usual places I say.