Several different federal agencies hold government auctions. The General Services Administration is the granddaddy of them all, because it sells on behalf of other departments. When a federal agency no longer needs something — say, a pickup truck — it reports the truck to GSA, which first offers it to other federal agencies and then to state and local governments or nonprofits. If nobody claims the truck, then the GSA auctions it off to the public, and you get your chance at it.
The majority of the vehicles found at local auctions will need some work done to them in order to be deemed “road-worthy.” Knowing this before you ever set foot on the grounds is a major part of deciding if this is the right way for you to source an automobile. A low bid on a crappy car has the potential to leave you stranded on the side of the road, so if you aren’t a savvy DIY wrencher, you’d better have one hell of a trustworthy mechanic.