When bidding on something valuable you should be careful when you loose a bid and you get a "second chance" with a buy it now at your maximum bid amount. It is fairly easy for a seller to make a deal with a friend who will push the price up to your maximum bid, and then that buyer wins the item. Shortly after the seller will make an excuse that the buyer retracted his bid and that you as the second highest bidder has got a "second chance" offer, usually very close to what your highest bid was.
It is hard to spot this, but some will in the last minute bid a lot e.g. raising each bid with $25 every try until they are above. You should ask yourself then this question, if the buyer really wanted this item so much that they bid several times just to try to get above you why all of a sudden did they change their minds? Chances are its the seller who has cheated you to get maximum price from the item.
The best way to avoid this is simply to not accept second chance offers, although at the same time since you are getting the item for your highest bid you really cant complain unless you are a man/woman of principles. I have sometimes accepted the second chance offers when I clearly see this "fake bidding" has happened and sometimes I have not (in which case the seller would most probably pass on the second chance down the line until he gets a buyer - after all he has to pay fees to list items).