Some auction rules have been changed today. I'll post the current rules here while the in-game rules page is being rewritten.

To start an auction, the following requirements must be met:
- Player must not be on loan.
- Player must not be on auction already.
- Player must not be included in any current transfer negotiations.
- Team must have less than 5 players already on auction.
- Team must keep at least 18 players not on auction.

To bid on an auction, the following requirements must be met:
- Team must have less than 49 players.
- Team must have enough money to cover the current bid AND all others its leading on.
- Team must place the bid before the deadline is reached.

Auction rules:
- The auction deadline is automatically set for 72 hours (3 days) after the auction starts
- The value of each bid equals the current bid + increment
- The increment depends on the current bid:
- For bids equal or under 5mil, the increment is 0.2mil
- For bids higher than 5 mil AND equal or under 8mil, the increment is 0.5mil
- For bids higher than 8mil, the increment is 1mil
- When a bid is made in the last 4 minutes before the deadline, the deadline will be set to 5 minutes after that bid. So there will always be 5 minutes between the last bid and the deadline.
- Bids are accepted during the last minute of the deadline. Ex.: Deadline is 15:32 -> Bids will be accepted up until 15:32 59 seconds.
- When the deadline is reached the auction will be closed and the player will move to his new team (if any) at the first minute of the following hour.
- Like on all other transfers, when signing a player on auction, the team will pay a signing bonus to the player equal to 4 times his wage (4*wage).

Auction Features:
- Managers will receive an FGM when they are outbid.
- Managers will receive an FGM when a player in their shortlist is placed on auction.

Added a new item to the rules list, its not a new rule but i forgot to include it on the original post. Its bolded and underlined.