Chances are you've been playing Monopoly wrong all these years, ignoring an official rule on property auctions.
And get this -- playing by the rule would actually make the game go faster!
If a player lands on a property and decides not to buy it, the property is supposed to immediately go up for auction to all players.
THE OFFICIAL RULES
"Whenever you land on an unowned property you may buy that property from the Bank at its printed price. You receive the Title Deed card showing ownership; place it face-up in front of you. If you do not wish to buy the property, the Banker sells it at auction to the highest bidder. The buyer pays the Bank the amount of the bid in cash and receives the Title Deed card for that property. Any player, including the one who declined the option to buy it at the printed price, may bid. Bidding may start at any price."