Here is how the scam works. There are variations, but the shopper gets hooked by a fake ad on a reputable website like Craigslist. When you visit Craigslist a scam warning greats visitors searching for cars and trucks for sale. But, sometimes the deal is too tempting to pass up - despite the warning. The interested buyer then emails the seller. The seller responds with a hard-luck story about a military deployment or divorce to explain why his price is so low. The scammer promises a money back guarantee and then the buyer moves the sale to another website masquerading as Kelley Blue Book. The buyer then sends payment to an escrow account that operates as a buyer protection plan and asks the buyer to fax them a receipt when it has been done. By the time the shopper figures out he's been scammed on a bogus website, the money is gone and so is the car.
Some scammers are extremely sophisticated, using 800 numbers and live chats with potential buyers to ease their concerns. Check out the domain name or the URL, which look very much like legitimate company sites.
Kelley Blue Book does car reviews and gives price information, but it does not sell cars or buyer protection plans.