In a lowest unique bid auction, the winner is whoever places the lowest amount that nobody else has bid. In a highest unique bid auction, it's the highest amount that only one person has bid. Bidders pay a fee for every bid, and the item can sell far below its value. This guide explains the rules, how BidKing picks the winner, and the legal question you need to answer before you launch.
The rules of LUB and HUB
A lowest unique bid (LUB) auction works like this:
- Every bid is a specific amount, such as $1.27 or $3.05.
- An amount counts only if exactly one bid has it. If two bids land on $1.27, neither counts.
- When the auction ends, the lowest amount that still has exactly one bid wins.
A highest unique bid (HUB) auction is the mirror image: the highest amount with exactly one bid wins.
Because a later bid can take away an earlier bid's uniqueness, the leader can change at any moment, and there can be no leader at all. A lowest unique bid of $1.27 stops being unique the moment someone else also bids $1.27, and the lead passes to the next unique amount, if there is one.
How BidKing decides the winner
Lowest unique and highest unique are auction types in every BidKing edition. For each lot you set:
- Lowest and highest bid allowed: bids outside this range are refused.
- Bid fee: what each bid costs from the bidder's wallet.
- Reserve (optional): the winning amount must reach it, or the lot ends without a sale.
- Start and end time.
Bids are in cents, so $1.27 and $1.28 are different amounts.
How BidKing works out the winner:
- On every bid, it recounts all valid bids on the lot and finds the lowest (or highest) amount that exactly one bid holds. That bidder becomes the leader.
- A repeated amount is accepted and charged like any other bid, but it isn't in contention. It also knocks out the earlier bid at that amount. Refusing duplicates for free would let anyone test which amounts are taken without paying.
- If no amount is unique, nobody leads.
- When the lot closes, the scheduled job works the winner out again from the bids themselves. Banned accounts can't win, but their bids still count when deciding which amounts are unique. If no unique amount belongs to someone who may win, the lot ends without a winner and the bid fees stay spent.
The winner then buys the item at the winning amount, through the cart.
What bidders see
- Each bidder sees only their own bids, each marked "unique", "not unique", or "unique but not the lowest" (or highest).
- A bidder learns whether they're in the lead. Others are told only that someone leads.
- The leading amount and the leader's name stay hidden until the lot ends.
If you show more than that, the game becomes easy to work out and stops being fair to people who bid early.
Bid fees, and why these formats are chance-heavy
The fees fund LUB and HUB auctions. If a $200 item sells for $3.41, the money comes from every bid placed, by winners and losers alike. That makes these formats very different from a normal auction.
- Most bidders pay and win nothing. Each bid is a paid guess, and only one bid wins.
- Skill plays a part, because bidders can study which amounts are taken in their own results. Chance plays a large part too, because no one sees the other bids.
- Losses can build up quickly. Bidders who chase a lot can place many bids, and every one is charged.
Be honest about this on your site. State the fee on every lot, explain that most bids don't win, and never present it as a way to make money.
Legal framing. A paid entry for a chance to win a prize is regulated as a lottery or gambling in many countries, and a unique-bid auction can fall into that category depending on where you and your bidders are. You, as the operator, are responsible for any licence, age checks and consumer rules that apply. Check with a local lawyer before you launch. In the UK, for example, the Gambling Commission regulates lotteries and gambling. BidKing requires sign-ups to be 18 or older, and you should not market these lots to minors.
Settings that keep it fair
- Publish the rules on every lot: the fee, the range, how uniqueness works, and what happens if no amount is unique.
- Set a sensible range. A narrow range fills up with duplicates quickly. A very wide one makes a unique amount easy to find.
- Think before adding a reserve to a LUB lot. The winning amount is usually low by design, so a reserve can turn most lots into no-sales while bidders still pay their fees.
- Keep staff and test accounts out. Don't let anyone who can see bids in the admin place them.
- Make sure cron runs, so lots close and settle on time.
Common questions
What is a lowest unique bid auction?
An auction where the winner is the person who placed the lowest amount that no one else bid. If two people bid the same amount, neither counts.
What happens if two people bid the same amount in BidKing?
Both bids stop counting. The second bid is still accepted and its fee charged, and the lead moves to the next unique amount, if there is one.
What if no amount is unique when the auction ends?
The lot ends without a winner, and the bid fees already paid are not refunded.
Is a lowest unique bid auction legal?
It depends on where you and your bidders are. Paid bids with a chance-based outcome are regulated as gambling or lotteries in many places. The operator is responsible for licensing, so check with a local lawyer before you launch.