The reserve auction has been an eBay character for a very long time, and though it continues to gradually decrease in popularity, there are still times when buyers find themselves bidding on an eBay auction for which a reserve price has been set.
(For those that aren't familiar with the reserve price feature, it is an option applied by sellers to an auction-format listing that excuses the seller from having to sell the item to the highest bidder if the highest bid doesn't reach a secret amount that the seller has supplied to eBay as their "minimum" amount for selling the item. More details are available for those that would like more help understanding reserve auctions.)
Unfortunately the reserve auction is often at the end of the day paired with that least desirable of phrases, "Reserve not met," the phrase that appears on auction listings when the highest bidder has not yet met the seller's reserve price, and the phrase that an appear when you have just placed a bid on a reserve auction.
Here's what to do if you are greeted by this phrase after placing a bid.
If the Auction Still has Much Time to Go
More specifically, don't bid on another auction listing for the item, assuming that you've not won this one, if you've used eBay's proxy bidding system (be careful, since you may have done this an not even realize it) and your maximum bid hasn't been reached, either. Other bidders could come along before the auction closes and bid against you, with your bid increasing in response to them. If this happens and one of your new bids exceeds the reserve, you are then on the hook for the item in question. If you've bid on another one in the meantime, you could be obligated to buy two of them.
Just as importantly, sellers can and often do return to reserve auctions that aren't performing well or generating as many bids as they would have liked in order to change or remove the reserve price. If this happens, the very same bid that a moment ago did not meet the reserve price may suddenly be the winning bid, and once again if you have bid on another similar item in the meantime and win it, you could end up on the hook for two of them.
Some buyers are tempted to retract their bids if they've bid on a reserve price auction and found that their bid didn't meet the reserve, but for both of the reasons above it's a bad idea to do so. There is also one additional reason for not retracting a bid when your bid didn't meet the reserve price: it's against eBay rules and doing so several times could get you banned from eBay.
If the Auction Has Finished with Reserve Not Met
If the auction has already finished and your bid never reached the seller's reserve price, you still have options. The first of these is to contact the seller and ask him or her if they're willing to sell this item to you at the maximum price that you entered into the eBay proxy bidding system (not necessarily the bid at which the auction closed). Though in a completed listing it's too late to remove or change the reserve price, there is no penalty for relisting the item without one, and eBay provides features to sellers to do just this.
If the seller is willing to do this, they can relist the item with a Buy It Now price at that level, inform you, and make the sale through eBay (to do so outside of eBay is a rules violation that could get them into trouble).
Your other option, of course, is to return to eBay and search for other, similar items that are being sold without a reserve price. This can often be the most desirable option if the item in question is the sort of item for which multiples are likely to be available on eBay, since it allows everyone to avoid the hassle and extra risk of dealing with reserve auctions.