The security deposit is collected in advance as an assurance that you will pay for what you purchase. All bids, once submitted, are final. If an auction ends with you as the high bidder, you will be obligated to purchase the vehicle for sale. In the event that you back out of the sale, your deposit will be forfeited.
Your deposit also determines your bidding limit. Your deposit should be a minimum of $400 or 10% of your desired maximum bid. Your security deposit is 100% refundable if you don't purchase a car.