Bidding mechanics in detail
The resolution algorithm written out, with worked examples, and an honest account of what the public bid history reveals about a sealed maximum, which is more than the phrase "sealed" suggests.
Two ways to bid#
| Maximum bid | Exact-amount bid | |
|---|---|---|
| You enter | The most you will pay. | A specific amount at or above the next minimum. |
| The price becomes | The lowest amount that wins, never your maximum unless it has to be. | Exactly what you named. |
| Your maximum becomes | What you entered. | What you entered. |
| Good for | Setting a ceiling once and leaving. | Making a statement, or jumping a bidding war. |
Both are binding. Bids are irrevocable offers and can only be raised, never lowered or withdrawn.
The algorithm#
Let M be the standing leader's sealed maximum and R the challenger's. inc(x) is the ladder step for a price of x.
| Case | New leader | New price |
|---|---|---|
| First bid on the lot | The challenger | The opening price (maximum mode), or R exactly (exact mode). |
| R > M: the challenger wins the proxy war | The challenger | min(R, M + inc(M)) in maximum mode, or R exactly in exact mode. |
| R ≤ M: the standing maximum answers | Unchanged | min(M, R + inc(R)). Equal maximums break for the earlier bid, which is the leader. |
Two rows are written in the third case: the challenger's bid at R, and the leader's automatic answer. One row in the other two.
Worked examples#
All on a lot standing at $1,000, where inc($1,000) = $100 and inc($4,800) = $100.
| Leader's max | Challenger bids | Mode | Result | Price |
|---|---|---|---|---|
| $5,000 | $2,000 | max | Leader holds | $2,100 |
| $5,000 | $4,950 | max | Leader holds | $5,000 capped at M, not M + inc |
| $5,000 | $5,000 | max | Leader holds; ties break earlier | $5,000 |
| $5,000 | $5,100 | max | Challenger takes it | $5,100 |
| $5,000 | $9,000 | max | Challenger takes it | $5,100 one increment over M |
| $5,000 | $9,000 | exact | Challenger takes it | $9,000 they named it |
Row five is the one that surprises people and it is the point of a maximum: bidding $9,000 against a $5,000 leader costs $5,100, not $9,000. Row six is the cost of naming an exact amount instead: you pay what you said.
Why the answer is capped at M#
In the third case the answer is min(M, R + inc(R)), not R + inc(R). Without the cap, a challenger bidding $4,950 against a $5,000 maximum would push the price to $5,050, above the leader's maximum, on a bid the leader never authorised. The house settles at the lowest winning price, and the lowest winning price against a $4,950 underbid is $5,000.
What is revealed#
"Sealed" is the right word for what the house publishes and the wrong word for what an attentive rival can infer. The house states the difference rather than letting a bidder discover it.
What is never published#
- Bidder identities. Bid histories show anonymised handles.
- Your standing maximum, as a number, anywhere in the bid history.
- Any reserve, before or after the sale.
What is nonetheless inferable#
-
An answer that is not exactly R + inc(R) is the leader's maximum. Because the answer is
min(M, R + inc(R)), a proxy response that lands short of the expected increment has been capped, and the value it was capped at is M. A probing bidder can binary-search a maximum in O(log n) losing bids. - A losing challenger's own maximum is published at face value. Their row carries R, visible. That is their bid, and it is in the record its own maker is entitled to.
- Where escrow collateral is on, the maximum is on a public blockchain. The lock equals the standing maximum plus the published fee schedule, so anyone can compute the maximum from the lock amount, permanently, and without needing to probe.
- Hiding the losing row would erase a real bid from the record, and leave an automatic answer standing against nobody.
- Publishing the losing row at the answer instead of at R would print a bid the challenger never made.
- Answering at anything other than
min(M, R + inc(R))either charges the leader above their maximum or hands the consignor less than the book supports.
So the mechanic stays and the promise was corrected instead. A maximum is sealed while it is standing. Once it has been beaten it is spent, and the price is the price.
The on-chain disclosure, and why the house accepts it#
The alternative is locking only the public price, and it does not work. A bidder takes the lead at $1,200 with a $5,000 maximum, withdraws everything above $1,200, and an hour later the timelock lets them claim it. The proxy then answers at $4,800 against collateral that has left the building, and the lot goes to a bidder the house cannot collect from.
Between a privacy cost the house can state plainly and an uncollectable winning bid, the house takes the privacy cost. Both halves of that trade are disclosed, in Conditions of Sale §2, in Privacy, and here.
Bid the exact amount you intend to pay rather than a maximum, or bid on a deployment where the escrow is off. There is no third option, and this documentation is not going to pretend otherwise.
What is checked before a bid is accepted#
| Check | Refusal |
|---|---|
| Repeat of an already-processed request | Returns the original ruling, never a second bid. |
Account suspended, or screened blocked / pending | Refused. |
Bid above the compliance threshold on a review account | Refused. |
| Bidding on your own consignment | self-bid. |
| Bidding from an account sharing the consignor's address | self-bid, with an audit row that survives the rollback. |
| Bidding on a consigned lot with no address on file | address-required, a precondition every bidder on the lot meets identically, which names nothing about the consignor. |
| Below the next minimum | below-min, naming the minimum. |
| Lot closed, withdrawn, or on an escrow hold | Refused. |
| Escrow position cannot be established | 503 backing-unknown. Fails closed. |
| The resulting close would outlive the collateral window | escrow-duration, naming the latest permissible close. |
| Erroneous or manipulative | The auctioneer may reject any bid. |
What a bidder gets back#
Every ruling, including a losing one and including a raise of your own standing maximum, mints a signed receipt. The raise path used to be the one bid decision that produced none, which was a gap in a site that promises a receipt for every bid decision.
A receipt binds the chain position, the resulting price, the outcome and the rules version, under an Ed25519 signature whose public key is published. You can fetch yours; anyone else fetching it gets the same ruling with the account masked and no signature. See Receipts and the event chain.
Reserves#
- Most lots are no reserve.
- A reserve is confidential and never above the low estimate.
- The system never bids on the seller's behalf at or above the reserve.
- A lot closing below its reserve is passed. With no bids at all it is unsold.
- The lot page states Reserve met or Reserve not met plainly, so a bidder always knows which side of it the current price is on, without learning the number.
Extended bidding, from a bidder's side#
A bid in the last five minutes moves the close to five minutes after that bid. It does not stack: two late bids do not add ten minutes. The total extension is capped at 30 minutes per lot, after which the close is fixed however many more bids arrive.
The practical consequence for a bidder: sniping does not work here. A bid at one second to close simply gives everyone else five more minutes. The mechanic exists to make a maximum bid a rational strategy rather than a disadvantage.
Buy It Now, and when it disappears#
Buy It Now on an auction lot is a winning bid: the buy price is the hammer and the auction house fee is added to it. It stops being available once bidding reaches 75% of the Buy It Now price, and it is never available during extended bidding, at that point the lot is in a live contest and a fixed-price exit from it would take the lot away from the underbidder mid-auction.
Where the escrow is on, that is the outer limit rather than the rule. Taking a lot outright closes it in the same transaction, so the collateral has to be standing before the sale is made, not fetched after it: Buy It Now is open only to the standing leader, and only while the buy price plus the fee on it is already locked against that lot, an hour or more clear of the lock’s expiry, with no other escrow operation on the lot in flight. Anyone else is refused with 409 escrow-bin-not-secured and nothing is sold.
Since a lock is the standing maximum plus the fee on it, the practical route to Buy It Now is to lead with a maximum at or above the buy price while the public price is still under the 75% line. A bidder who cannot do that has not lost the lot; they bid for it like everyone else.
Fixed-price Buy Now listings are a different thing entirely: no fee, no auction, and the listed price is the full price.