You should listen to your common sense. For all you know this could be a stolen vehicle, registered to someone else or even have a lien against the vehicle....
It isn't difficult to obtain a new title when the owner has lost theirs.
Tell him to apply for a new one.
http://www.dmv.org/wy-wyoming/replac...lost-title.php
If he isn't willing to do that, then there is a reason.