on 09-27-2012 12:51 PM
What you're seeing isn't a hidden reserve set by the seller and the immediate outbid isn't the seller trying to raise your price.
Other responders may tell you about the eBay Reserve price option, but that's not what you're experiencing. If the seller has set a Reserve on the auction, the listing page will show the words RESERVE NOT MET immediately below the Bid box.
You're bidding against the current leader's unrevealed full bid. Unlike the classic going, going gone auction where every bid is taken at face value, on eBay, you can bid as much as you're willing and able to pay, but on eBay if you are the leading bidder, your current showing bid will only be at most one bid increment over the second highest bidder's full bid.
The leading bidder's actual placed bid is kept secret until it's needed to respond to another bid. When you see a top bid amount of, say, $4.99, that's not the leader's full bid. They might have bid $20, $100 or even more if they think the item's worth that much.
If you bid the minimum required amount that eBay states in the listing, you're likely to be outbid by the leader's unreveal full bid.
Whatever you bid, eBay will compare your bid with the leader's unrevealed full bid. If your full bid is less than the leader's unrevealed full bid, ebay will immediately tell you you're outbid and automatically reveal your full bid and set the higher bidder's showing bid to one bid increment over your full bid.