Wikipedia:
The chargeback mechanism exists primarily for consumer protection. Holders of credit cards issued in the United States are afforded reversal rights by Regulation Z of the Truth in Lending Act. United States debit card holders are guaranteed reversal rights by Regulation E of the Electronic Fund Transfer Act. Similar rights extend globally, pursuant to the rules established by the corresponding card association or bank network.
A consumer may initiate a chargeback by contacting their issuing bank, and filing a substantiated complaint regarding one or more debit items on their statement. The threat of forced reversal of funds provides merchants with an incentive to provide quality products, helpful customer service, and timely refunds as appropriate. Chargebacks also provide a means for reversal of unauthorized transfers due to identity theft. Chargebacks can also occur as a result of friendly fraud, where the transaction was authorized by the consumer but the consumer later attempts to fraudulently reverse the charges. Card association chargeback rules (e.g., MasterCard) are available online for public inspection and review. They comprise a system for adjudicating transaction disputes between cardholders and merchants,[1] primarily where the issues can be resolved based on documentary evidence incident to the transaction. The rules provide for arbitration of issues by the card association. This may occur where the card issuer generates a *second (or "arbitration") chargeback* against the merchant, after receiving the merchant's response to the initial chargeback. Normally this would require the cardholder to rebut elements of the merchant's response. The second chargeback results in a second crediting of the cardholder's account for the disputed funds, after having been credited back to the merchant with its response to the initial chargeback. The merchant's only recourse after the second chargeback is to initiate arbitration of the dispute by the card association. The fee for this is in the order of $250, and the arbitration loser is then obligated to pay the costs of the arbitration.