Arbiter

• clear-unauthorized-chargeback

  Reg E card-not-present fraud, AVS+CVV fail, no merchant evidence → chargeback, cardholder wins.

• friendly-fraud-strong-evidence-deny

  Reg E non-receipt with strong merchant compelling evidence → deny / representment-upheld, cardholder liable.

• timeline-breach-forces-provisional

  Red-team: card-present ATM withdrawal (weak merits for the cardholder) but the bank missed the Reg E provisional-credit clock → provisional-credit is mandatory regardless of merits.

• ambiguous-regz-deny-with-basis

  Reg Z defective-goods billing error, merchant rebuts, no evidenced defect → deny with documented basis.

Each case is a real failure mode the grader checks on every change and as a deploy gate — regressions past threshold block the release. Adversarial cases probe the failure modes the golden set doesn't.

Briefing

• Adjudicates cardholder disputes under the governing regime — Reg E for electronic transfers, Reg Z for credit billing errors — on the evidence and the clocks.
• The timeline dominates: it checks the regulatory clock before the merits, and a breached provisional-credit deadline decides the case for the cardholder no matter how strong the merchant's evidence looks.
• On the merits it applies the regime's own tests — failed address and card-code checks on a card-not-present charge point to fraud; delivery confirmation, prior undisputed use, and a matching IP point to friendly fraud.
• Records the ruling with the liability party and auditable reason codes; the record itself moves no money.