I post this because there is not a single instance of the officially correct rules in English here on BGG. One or both of the following two issues is incorrect in all of the rulebooks found among the uploaded files.
There are two things in the rulebook of the Mayfair edition that differs from the official rules in the German, 2009 Pegasus edition. The rulebook in this latter edition is completely confirmed by Reiner Knizia. This was said to me by the company that has made the rulebook for that edition. You can check the German rulebook for yourself: http://www.pegasus.de/1732.html
1) Money flow in case of a Double auction card The player who adds the second card and auctions both cards receives all of the proceeds from their sale. 2) Who turns the top card of the virtual player in a three-player game In the course of an auction round, the player who wins the bidding may turn over the top card of the virtual player.