Can you buy a house at an auction if you have bad credit?

Sure if you have cash. All auctions are cash or certified checks.

You can buy anything, it's borrowing that is a problem. How will you pay for the house?

Most auctions require payment on winning the auctions, so you would have to go to the auction with the money. You might want to look into HUD houses that are for sale for $1.00. Most of them are in need of massive repair, and you have to sign an agreement that you will do the repairs in a certain amount of time.

If you pay cash

If you have cash

You'll need bank backing to enter any auction for real estate - where I come from anyhow.

If you have the cash, no one will even ask about your credit.