The United States Government has a policy that the cars of their agencies and departments can only be used so long. After they finish their service life, even if they are in great condition, they must be retired, and replaced by a newer model. When a government vehicle is retired, it is disposed of by way of a public auction where members of the public can bid on and purchase the vehicles.
Government auctions are held in all fifty states because the government has fleets stationed in every state, for the use of its agencies, and they do not want to have to transport retired vehicles to one central location for auction. The auctions are held several times a year, because vehicles are always reaching the end of their service life.
Before a government auction starts, you are allowed to inspect the vehicles that are going to be auctioned off, to see if they have any serious problems that may affect function or safety. This is rare because government vehicle are well maintained, and kept in top condition. It is advisable to bring someone who knows about cars to the auction with you to check them out if you are not mechanically inclined.
When the bidding starts, it starts cheap. People bid on the cars until someone is the high bidder, and that high bidder takes the car home for the price of his bid, no matter how much below the retail price of the car his bid is. Most of the time, the final bid is several thousand dollars less than the current value of the car, and sometimes it dips drastically lower than that.