Shill bidders often 'nibble bid' up to just over the highest bid that has been placed. They then withdraw the bid leaving the highest genuine bid in place. The person with that bid will get the item at their highest they bid if it wins. They will not get it cheaper at any of the bid increment stages as the shill bidder has increased those levels.

Bid late and at your highest is sometimes the best way to win an item at the cheapest price