Poll- Declaring a vehicle for less then you sold it, Will my friend burn in hell? Options

[highways]

So this isn't for me, but a friend selling an expensive car, and finally they found a buyer. Thing is buyer is asking for some help by declaring the vehicle for about half of the sale price. Car is rather new and not cheap. Friend wants to help buyer (mostly just to get the damn thing sold, it's been forever) but also is scared of the legality of reporting low figures to DMV. I'm doubly worried for them because it's a fairly new car and the value would be pretty well established I'd think. What's the skinny?

Edit:
Also this buyer is saying that some bonified dealers have been extending this 'arrangement' for him under the pretense that another car was traded, hence the low money value exchange. Could this be true? How's a private seller supposed to compete with dealers who pull this stuff?