Marketplace facilitator

Every US state with a sales tax makes a qualifying marketplace the party liable to collect on its third-party sellers' supplies. Missouri closed the set on 1 January 2023. The EU does the same through the Art. 14a deemed-supplier rule for electronic interfaces.

Where that applies, the seller charges nothing. A seller who charges anyway double-charges the customer on every marketplace order.

new TaxQuery(
    // …
    marketplaceFacilitated: true,
);

Document-level too — the facilitator relationship is a fact about the transaction, not about one product on it:

new TaxOrder(
    // …
    marketplaceFacilitated: true,
);

It is not "exempt", and the difference lands on a return

Four treatments produce a zero charge and they mean opposite things:

Most states still expect the seller to report the sale in gross receipts and then deduct it as marketplace-facilitated. A treatment that collapsed these would file a wrong return while charging the right amount, so taxWasDue() is what a filing asks rather than chargesTax().

Only you know it happened; only the data knows if it applies

Whether a given platform qualifies as a facilitator, and whether it has taken on collection for this supply, is a fact about a commercial arrangement. Nothing in a rate table can answer it, so the engine takes your assertion.

It then checks the law, on the supply's date. A Missouri sale from 2022 predates the rule and is still the seller's to collect — answering from today's map would zero a charge that was really owed.

Two states carry no date and therefore never apply it. Arizona's published figure predates its marketplace act by three years and looks like an earlier remote-seller provision; Alaska has no state sales tax to hang one on. Both leave the tax with the seller, which is the recoverable direction: charging twice is visible to the customer and refundable, charging nothing surfaces in an audit years later.

What still decides

Taxability. A marketplace collects nothing on an exempt supply, so an exempt line is reported Exempt for its own reason rather than credited to the marketplace.

Not your nexus. The check runs before the seller's own registration, because the marketplace's liability is not derived from the seller's presence. A seller with no nexus in the state still owes nothing on a facilitated sale — and the reason says why, where NotRegistered would have said something else entirely on the same zero.