Bid sniping – including the use of software that places bids for you – is allowed on eBay, but it doesn't guarantee you'll win an auction. Other members may be using the same tactic, could have set up automatic bidding, or may simply react quickly and place a higher bid before the auction ends.
Instead of bid sniping, you can set up automatic bidding for items you want for listings where you want to maximise your chances of winning.
Automated bid sniping software
Many websites and software packages offer automated bidding based on the end time of an eBay auction. They try to place your bid automatically just before the auction ends, and some try to synchronise with eBay servers to make sure your bid is the winning one.
When you sign up with third party providers that offer automated bidding, you should make sure they are trustworthy before entrusting them with any personal data, like your eBay password. Remember, you're responsible for any information you give to third party services.