Bidding Process & Bidder Details

Client has a very common scenario, which is the bidding process. All the property which is sold out or leased out is first available for bidding. The bidding is done and bidders submits their bid amount. Once the bid is open, the highest bidder is selected and the rest will get their bid security back as refund. The selected bidder is selected as customer and then ask to pay the complete amount.

The concern here is the quantum of customers. My client has some times around 5000 to 8000 bidders. Kindly reply with any appropriate solution for bidding. And how the bidders will be treated. Will they be treated as customers? if yes, huge time will be required and it will ultimately increase the customer database. Or if misc receipt is entered, how we will refund the payments to the bidders.