So he paid retail price ($40K) and then traded it back in for $27.5K a month later. The trade-in was beat-down because of the CarFax. So the dealer sold the truck for a 15% profit, bought it back for 30% less a month later and will probably resell it for about $34K or a 15% profit on the buy-back.
CarFax told the buyer a story and he believed it. The dealership told him a story when he brought the car back a month later and he believed it. Then he accepted the deal.
The dealership played this game far better than the buyer did.