Arbitration (card disputes)
The last stage of a card dispute, where the network itself rules between issuer and acquirer and the loser pays both the amount and the bill for the ruling.
A dispute starts as a chargeback, meets the merchant's representment and may escalate to pre-arbitration. If neither side backs down there, one of them can take the case to the network. Visa and Mastercard each run an internal body that reads both sides' documentation, applies the network's rules and issues a decision that generally can't be appealed.
What decides how often this happens is the price tag. The network charges a filing fee, often several hundred dollars, and the loser pays it, with penalty fees on top for anyone who broke the rules along the way. For a disputed purchase of thirty dollars the arithmetic is obvious, and most disputes are in practice settled by whoever does the maths first. What reaches arbitration is mostly large amounts, or matters of principle between banks that deal with each other a lot.