The police.
You can go to the police.
The scam should be reported to the company you are making the transaction through or to the police.
There are many ways in which one can find auctions for police cars. This includes checking for local ads in their paper as well as looking on car sites such as AutoTrader.
government auctions
Attending police auctions is a way to buy cars from the government or law enforcement.
Government auctions are usually held by police precincts. If you call your local precinct, they can tell you when and where they are holding auctions.
You can buy repossessed automobiles in the U.S. through many county auto auctions or police auto auctions. Check with your local courthouse or police department to find the next auction.
Motorbikes regularly come up at auctions across the entire country. There are at least 300 auction houses in the UK alone, the largest being Manhiem and British Car Auctions. Many of these will sell bikes entered by various police authorities. Note, individual police forces do not sell goods. All items are sent to contracted auction houses. You will need to find a directory which lists all auctions houses that deal with the police authorities For more information, see Sources and Related Links.
In many areas, police and local governments will hold vehicle auctions. Thrift stores and local charities are also excellent sources for auto auctions, which are generally held regularly.
Online auto auctions like eBay Motors auto auctions and Yahoo Auctions. Basically private sellers and junk car sales. Wholesale auto auctions is generally where dealers buy used cars from other dealers to try and sell on their lots. Public auto actions is everyone for themselves. This goes the same with the cars. Good, bad and ugly but anyone can buy them. Public auctions have the most scam potential though. I trust police, government and insurance company auctions the most. Police and government are high mileage old cruisers or transport cars but at least you know they have been maintained over the years. Insurance and salvage company auctions are usually only open to dealers but sometimes they are public. These are just cars people couldn't afford so it runs the risk of not knowing how they were treated but insurance agencies are going to be at least somewhat honest about it and wouldn't sell a lemon.
www.usa.gov has a comprehensive list of government auctions, though local government auctions are not included, only federal. You will have to talk to your local municipality or police station to find out about local government auctions.