Are they Legit? Would you do it? http://www.gov-auctions.org/join.php
However you have to take into consideration that if someone had their car seized, they probably weren't upstanding citizens, and may or may not have cared about the proper maintenance and care of their vehicle. (Same goes for repos).
They are probably all checked out to make sure they are functional and safe, but that doesn't necessarily mean they won't have serious problems down the road.
I would say don't participate in such auctions unless you know exactly what you're doing, and can at least inspect the car mechanically.
You can find thousands of different auction and repo cars really cheap at http://www.carauctions.co.nr , its the best online site , it comes with a 60 grantee
Hope this helps