Pete, That is an interesting question. I personally won't bid against certain friends when they are high bidder, BUT as soon as they are no longer the high bidder, the item is fair game. The real problem occurs near the end of auctions, on chips that I really want, where the high bidder is a friend. He could easily be overbid at the end and someone else may end up with the chip at a lower price than I would have bid. I have had that happen to me.
Usually,I just sit back and not participate in that auction.