Avoid collusion in bidding systems 

  It is one of the biggest drawbacks of a bidding system. You could speed the process up and it can cut down some of it in limiting the time .

  It would be a tough thing to prove but if you could you can remove the player doing it ands send a strong message to those considering it.It might be possible to find patterns of collusion after the fact. You could, say, look at the average costs of first items and decay in cost of certain items and see if there's a certain class or raid role that ends up with a trend that does not fit in with the other ones. Warning: You will have a pretty small sample size, so no trend may ever be identifiable.

  And if you REALLY wanted to be a hardcase about it you could sanction people with their future bids. Maybe if you've found that damage casters have colluded on their bids, you set a new minimum for their items.

  Realize that this is probably a nuclear level of thing to do, and will likely irreparably damage your guild. It may be worth tracking to find out if anything does come out, but doing something about it is pretty rough. Raising minimums will not hurt the people who have enough points to collude, it will hurt the people who don't raid as much, or come in to your system late.

  Personally, that's the exact reason I prefer fixed-cost systems over bid systems. There are definitely other drawbacks to fixed-cost systems, but in my opinion they're built into the system, and are obvious on the face, not something that would undermine it from secret.