Complaints about such practices are rising, but there isn't much a buyer can do: if the dealer has gone bankrupt, mere scraps are rewarded to most folks in the scrum of creditors. Most states have insurance bonds against these kinds of losses, but they might pay as little as $5,000, which is barely enough to cover one default.
Ohio, Virginia, and West Virginia have restitution funds. California -- exceptionally victimized by the practice because of the number of cars sold in the state -- is creating one that will be fed by a $1 fee on every car sold, but it isn't operational yet. In the meantime, used car buyers should ask to see the car's title to ensure it's clear. And for all buyers, in good times and especially in bad, caveat emptor.