If you intend to double-sell* the item, you'll need to edit the quantity to 2 in order to sell to the second bidder. Be aware that the quantity is displayed in the web catalog so you may want to edit the quantity just prior to (or even during) your event.
* Double-selling is when the auctioneer conducts bidding as high as possible with the final two bidders, then asks both bidders to buy at that price if the donor will "agree" to donate another. For instance, two bidders remain and the last bid was $1200. The high bidder appears to have reached their "limit". Instead of asking the other bidder to raise it to $1300 - the auctioneer would offer to sell one to both bidders for $1200 each. A good auctioneer will make this look like a spontaneous idea - but it has usually been pre-authorized by the donor (and the auctioneer is aware of items that can be double-sold).
To offer online pre-bidding on Live items, clone the live item, then edit the cloned item to type = Silent, and set it for bidding pre-event online, paper at event (this prevents the item from being awarded at closing). Once online pre-bidding has concluded, edit the cloned item to quantity = 0, and provide your auctioneer with the high online bid for use as the starting bid.