These have been left prior to the lot coming under the hammer, and will normally be bid by an auctioneers clerk. If you find that you are the only person in the room bidding, and the price is still rising you are probably against a 'commission' bid. Telephone bids are also becoming more widespread. Again an auction house employee will be on the telephone bidding against you. The other thing you need to be aware of is the 'reserve'.
Some vendors enter an item into auction with a minimum price tag, known as the reserve.
If the item does not reach the reserve, the auctioneer will inform the room, and it is not sold. Once all your lots have passed, pay your bill, obtain your receipt, find yourself a porter, and ask for your treasures. Make sure that you are given everything that you have paid for. View your lots. Decide on your bid limits.