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Self-trade prevention on event venues

If you place both a buy order and a sell order in the same market, there is a chance they could meet in the order book. Most regulated venues stop that from happening through self-trade prevention, or STP. It is a small technical feature, but it affects order workflows, automated tools and the reliability of volume data. This SoftCta guide explains how it works.

What a self-trade is

A self-trade occurs when an incoming order would match a resting order from the same participant. The result would be a trade with no real change of ownership. On a regulated venue, deliberately trading with yourself to create the appearance of activity is a form of wash trading, which is prohibited. Our wash trading guide explains why it distorts markets.

How STP modes work

Venues that offer STP typically use one or more modes:

• Cancel newest: the incoming order is cancelled and the resting order stays.
• Cancel oldest: the resting order is cancelled and the incoming order continues.
• Cancel both: both orders are removed.
• Decrement: the larger order is reduced by the size of the smaller one.

Some venues apply one default; others let API users choose a mode per order. The behaviour matters for anyone using automated tools, because an order may be cancelled without warning. Our guide on cancel and replace workflows covers related mechanics.

Interaction with matching

STP sits inside the matching engine. When an incoming order would hit your own resting order, the engine applies STP before matching against others at worse prices. Under price-time priority, cancelling a resting order means losing your place in the queue.

Why ordinary users notice it

A user switching sides, for example placing a sell order at a price where they already have a resting buy, may see one order disappear. On venues that represent Yes and No as complementary positions, a No buy can be economically similar to a Yes sell, and the venue's rules determine whether STP treats them as opposing. Read the help documentation before assuming an order failed for another reason. Our guide on limit and market orders explains order types.

Scope across accounts

STP may apply within one account, across sub-accounts or across all accounts linked to a firm. On some crypto-settled venues, separate wallets controlled by one person may not be linked at all, so STP cannot catch everything. That is one reason why reported volume can include activity with no real economic transfer.

Volume literacy

Because STP is not perfect and not universal, high volume does not always mean genuine interest. Our guide on suspicious volume gives habits for reading activity.

A reading habit

Check whether the venue documents STP, which mode applies and its scope. If you see an order cancelled unexpectedly, look at your own resting orders first. Use the fee drag tool to understand costs of repeated cancels and re-entries, and verify live prices on the venue.

Primary sources SoftCta readers open

• Venue API documentation on order types and STP
• Venue rulebooks on prohibited trading practices
• CFTC guidance on wash trades
• Exchange notices on matching engine changes

Reading the quote step by step

• Read the full title and rules, including the named settlement source and the time zone.
• Convert the Yes and No prices to implied probabilities and note the gap between them.
• Subtract fees and spread to see the effective price you would actually face.
• Write your own probability range and the evidence behind it, then compare.
• Check related and near-duplicate markets on other venues for consistency.

Closing SoftCta checklist

• Re-read the venue definition in your own words before reacting to a price.
• Convert prices with fee and spread awareness; verify live cents on the operator.
• Prefer primary settlement sources over secondary headlines and social summaries.
• Treat ChanceWire hubs, movers, and tools as orientation — not order entry.
• Confirm age, location, and product eligibility; SoftCta pages will not suggest location spoofing.
• If clarity is incomplete, watching is a complete SoftCta outcome — no pick-selling urgency required.

SoftCta habits

• Write your own probability range before checking the crowd price.
• Prefer dated primary sources over social summaries.
• Compare related markets when a single book looks extreme.
• Size curiosity with fees and depth in mind; substantial risk of loss.