Warning: like so many laws this area of law is constantly changing.  It is your responsibility to confirm the latest version of the law.
ARS Section 33-810 (A). On the date and at the time and place designated in the notice of sale, the trustee shall offer to sell the trust property at public auction for cash to the highest bidder. The attorney or agent for the trustee may conduct the sale and act at such sale as the auctioneer for the trustee. Any person, including the trustee or beneficiary, may bid at the sale. Only the beneficiary may make a credit bid in lieu of cash at sale. The trustee shall require every bidder except the beneficiary to provide a one thousand dollar deposit in cash or in any other form that is satisfactory to the trustee as a condition of entering a bid. The trustee shall not refuse cash as a form of payment of the bidder’s deposit.
Every bid shall be deemed an irrevocable offer until the sale is completed, except that a subsequent bid by the same bidder for a higher amount shall cancel that bidder’s lower bid. The trustee shall return deposits to all but the bidder or bidders whose bid or bids result in the highest bid price.