Your question is a little vague.
There are several types of real estate auctions.
A quick answer is "no", cash is not necessarily all that will be accepted.
But, you should be totally pre-approved for financing if that is what you need.
Do not bid unless you know you can pay cash or be totally backed by your lender.
There are HUD silent auctions that you must enlist a licensed real estate professional
to submit confidential bids for you on foreclosed properties.
There are the county Sheriff Sale auctions for foreclosures.
There are private auctions where the bidders are specific invitees.
One of the most popular are the public auctions performed by professional companies.
This includes Rose Auction, Hudson & Marshall, Williams & Willams, etc.
Each have their own criteria and requirements but basically you need to
have proof of funding, a large deposit in a cashiers check, and the ability
to complete the purchase in a few days (sometimes hours depending on the auction).
You should have the understanding that there will be a percentage tacked on to your bid for commissions.
Some of these auctions are done online and go on for several days,
so you have a chance to change your bid to try to obtain the property.
Other auctions that are in person, are over in a matter of minutes.
I am a real estate agent certified to perform bids for my clients.
For real estate questions check the web site below or contact:
Cell (248) 931-0084
REAL ESTATE AND FINANCE IN ONE
34 S. Telegraph Rd
Waterford, MI 48328
Office (248) 886-0000