After watching an item I was considering bidding on rapidly exceed the "Buy -it Now" price half an hour before the auction closed I thought the following might be useful.
Do your research.
How many times have we heard these words, it is especially true in auctions, how much does the item I'm bidding on retail for? How much is the postage for each item I am bidding on (it may be the same item but different suppliers may charge different postage)? Is insurance included in the postage cost & if not is insurance mandatory (i.e. extra cost)? What is the Buy-it-Now price through different vendors on eBay? The answers to these questions will give you an idea of what your maximum bid might be.
Set a Maximum price you want to pay for an item & stick to it.
After doing all that research, you have come up with a maximum price you are willing to pay for your item. You must have had a good reason for setting this price, maybe because it is within your budget, it is the price of the goods (including postage & insurance) from a retailer, or it is retail less 20% - whatever the reason stick to your maximum.
Beware of the gazzumpers. These are the individuals that wait until the auction has almost closed to place a bid. This might also be the time at which you may wish to formaly enter your final maximum bid (see above).
Don't enter your final maximum bid early in the auction. This can provoke a bidding war where other bidders try to find out just how much you are willing to pay. You may see in the bid history a lot of successive entries by the same person. The consequence of which will be to bid the price up closer to the maximum amount you wanted to pay ie everyone except the seller misses out on a bargain - and isn't that why you are in an auction - for a bargain?