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 33-811(A) If the highest bidder fails to pay the amount bid for the property the trustee, in his or her sole discretion, shall either continue the sale to reopen bidding or immediately offer the trust property to the second highest bidder who may purchase the trust property at that bidder’s bid price.
The deposit of the highest bidder who fails to pay the amount bid shall be forfeited and shall be treated as additional sale proceeds. If the second highest bidder does not pay that bidder’s bid price by 5:00 p.m. of the next working day then the trustee shall either continue the sale to reopen bidding or offer the trust property to each of the prior bidders on successive working days until a bid price is paid.
A highest bidder who fails to pay the amount bid by that bidder is liable to any person who suffers loss or expenses as a result, including attorney fees, plus that bidder may be black-balled from any future trustee sales.