not true. maybe some slip through the cracks but they will send out a letter if they review it and see you paid well under what book value is.
did it to me.. i bought a truck from a neighbor for $250. titled it and no questions right then and there but a month or two later i get a letter saying i paid way less then book value and i needed proof from the seller that all i paid was $250. no problem the seller was my neighbor so he signed what he needed to sign and i was good to go..
they have been doing it for years now. 10-15 years that i know of. i personally know a couple other guys that had the same thing happen to..
from there on out i always get a receipt when i by a car or write a receipt when i sell a car. some times we will write up two receipts . one real one and one for the dmv.. :)
in this day and age you have to be nuts not to get some kind of bill of sale when buying a car.