  We introduce a general approach based on \emph{selective verification} and
obtain approximate mechanisms without money for maximizing the social welfare
in the general domain of utilitarian voting. Having a good allocation in mind,
a mechanism with verification selects few critical agents and detects, using a
verification oracle, whether they have reported truthfully. If yes, the
mechanism produces the desired allocation. Otherwise, the mechanism ignores any
misreports and proceeds with the remaining agents. We obtain randomized
truthful (or almost truthful) mechanisms without money that verify only $O(\ln
m / \epsilon)$ agents, where $m$ is the number of outcomes, independently of
the total number of agents, and are $(1-\epsilon)$-approximate for the social
welfare. We also show that any truthful mechanism with a constant approximation
ratio needs to verify $\Omega(\log m)$ agents. A remarkable property of our
mechanisms is \emph{robustness}, namely that their outcome depends only on the
reports of the truthful agents.
