Always destroy your bidder number card when you're through buying. If you carelessly dispose of it, your card may be picked up by someone and used without your knowledge. Although it isn't common to clap or show extreme emotion when an item sells, sometimes all that built-up adrenaline needs release. I once attended an auction where an original Brewster C-spring Victoria in mint condition came up for bid. The bidders were professionals, and the bidding was hard and fast, so I never got to see who was bidding or who won the final bid.
Auctions are exciting.