Sean is right. Placing a bid above the (unknown) Reserve price will cause your bid to be accepted at the Reserve Price. That is true even if the auction ends and your bid was the only one placed.

It's not recommended by ebay but that's one way to discover the reserve on an auction. Place a high bid and see at what price the bid is accepted. Then cancel your bid. However, ebay keeps track of members who cancel a bid too often and you may be warned or barred from bidding in the future if you do it regularly. Not suggested!

A Reserve on an ebay auction benefits only the seller. Some sellers use this to try to discover demand for an item they're not familiar with. Note that if their auction ends with a bid but Reserve Price is not met, ebay allows them to use the "Second Chance Offer" to offer to sell at a price lower than Reserve.

Psychology also enters into the decision of whether to Reserve or not. A lower starting bid (like 99c) with a Reserve may stimulate enough interest to get bidding up to the Reserve while setting the starting bid at that level may get no bids at all. Then, there are some of us bidders that won't bid on Reserve auctions on general principle .