I have already gone through why you should NEVER buy a car from the auction. But if you're feeling brave and you're savvy you can save a lot of money by buying through the auction. I highly suggest you read my other article on why you have no business there before reading this one.
Do your homework:
If you are looking for a specific kind of car, go to the forums and read about the various common problems of that vehicle. Create a checklist of things to look out for regarding that specific make model and year of car. When you are at the auction you will get caught up in the excitement of the auction and your animal brain will grab hold. You will see the right car in the right color and get carried away. Make sure you have a checklist.
Don't be too picky:
Picky is a good thing when it comes to condition but If you are hung up on a color or a certain model package odds are you are going to be disappointed. You can be as persistent as you like but auctions are filled with the beige Camry 4 cylinder automatic of your dreams.
Be realistic, and honest with yourself:
Write down your MAXIMUM price on a piece of paper. Put it in your pocket. DO NOT go over that number. That is your hard limit. Don't get caught up in the excitement, stay firm on your number. That said, make sure that number is realistic. Kelly blue book or NADA are nice places to start but they do not reflect the honest value of a vehicle. Soft market cars such as Buick's go for less and Toyota Tacoma's can go for near or in strange cases, more than KBB.
Don't forget the fees:
Auctions charge a fairly hefty fee in addition to the sign up fees. Typically these fees are in the range of 500-1000 dollars which are based on the selling price of the vehicle.
I highly recommend buying "Green light" cars. These cars have a "warranty" of sorts. Different auctions do this differently\, but generally you'll be allowed an hour to evaluate the car and drive it. If something can be proven to be out of whack or you feel you have been misled you can appeal tot he auction for help or return the car. While this doesn't always work it is better than the nothing you get with a "red light" sale.
Red Light sales are the ones you really have to look out for. Red Light sales have the largest risk. This is where the big savings are but it's also where the big losses are. The car could explode into flames right after the gavel drops and you own not only the remains but the damage it causes the auction. I don't recommend these to anyone, even the dealers get burned by these on a regular basis.
A lot of auctions also have a service where they will, for a fee, inspect the vehicle and give a condition report. You should take advantage of this if possible before removing the vehicle form the property.
Make sure to insure the vehicle before you take it off the lot and make sure you have a clean title in your hot little hands before putting any money into the car. Every so often something goes wrong with the paperwork and if you have put a new engine in the car you are now out of not only the new engine but all the labor you put into it.