What is the ruling on the insurance paid before an auction by someone participating in it, and what is the ruling on postponing the payment of the remaining amount after the auction is settled?

The guarantee requested by the supervising authority for the auction is permissible if it is returned to those who did not win the bid, and is counted as part of the price for the one who won the deal. Requesting a guarantee from those who wish to enter the auction is Islamically permissible. As for paying a portion of the bid amount in cash and the remainder as a debt, this is not usury, and there is no harm in it if it is by mutual consent of the seller and the bidder.