Geez, £1 for landing on Free Parking is awfully cheap. Unless you're talking REAL money...

The auction thing is in the official rules (at least in the U.S. version), but I think most people never realize it because they never actually read the rules, having learned how to play from someone else. There's all sorts of minor things people never notice. Like you can never have more than 32 houses or 12 hotels on the board at any one time (the amount that originally comes with the game).

I usually play the iron, though sometimes I play the hat. I have no idea why...

As a bit of trivia, Monopoly as we know it today is largely based on an earlier game invented by Elizabeth Magie Phillips.
http://en.wikipedia.org/wiki/History_of_the_board_game_Monopoly