Most auctions open to the public demand payment right away...as in they usher you to the payment window right away before you can change your mind.
If you don't know what you are doing, you may be screwed.(Unless you are a mechanic) Most cars at public auction have none or 1 real bidder, Its just the auctioneer looking for idiots and if you bid, he will try to get you to keep bidding until he reaches the sellers price or there is no sale and the auction doesn't make any money.
Very few "good" cars are sold on the auction block at public auctions.
While there may be a few good cars there, the sellers are usually dealers who are looking for a nice profit and simply wont sell it if someone doesn't pay that amount.
The dealers that do work public auctions tend to do so for "leads". That is, the people will tend to come back the next day or the next week and buy it or something else because they were disillusioned with the auction process and feel better paying UP for a good car.
Most cars that SELL on the block at public auction's are cars that LOOK good but have hidden problems and are sold as-is.
After you pay for it, you can find out what problems you bought.
I was a dealer for many years. Most times, my cars brought more at dealer only auctions than public auctions.
At dealer only auctions, there is MONEY there. At public auctions, there may be 60 cars & 6 buyers with money.