Your Proxy Bid amount is the maximum amount (highest price) you are willing to pay for an item.

You should determine beforehand the most you are really willing to pay for an item and then enter a single bid at that amount in the Bid Amount field. Your maximum bid amount will not be shown to other bidders but will be used with our Proxy Bidding system to place bids automatically on your behalf.

Lowest Successful Price:

The goal when using Proxy Bidding is to win an item at the lowest successful price. To do so, you must be the bidder who placed the highest maximum bid at auction close. The lowest successful price may not necessarily be the maximum bid amount you submitted to win the auction, unless there was a tie. Typically, the lowest successful price is the next highest bidder's maximum bid amount plus the stated bid increment.

Bid increments are the lowest increment between bids allowable on individual auctions. Bid increments are listed on the product detail page where you place your bid and are typically $1, $3 or $5.

Please Note: Proxy bidding is ONLY recognized in regular auctions and in  Reserve Price auctions where the reserve has been met. You can view a tutorial on proxy bidding Here