here is a good study on that [pdf] http://www.cramton.umd.edu/papers2000-2004/00jre-collusive-bidding-lessons.pdf http://www.cramton.umd.edu/papers2000-2004/00j

here is a good study on that [pdf] http://www.cramton.umd.edu/papers2000-2004/00jre-collusive-bidding-lessons.pdf http://www.cramton.umd.edu/papers2000-2004/00jre-collusive-b... Essentially people try and convey information to the other bidders through the amounts of their bid. Like putting an area code at the end of a large bid to indicate that is the market you want.