In the credit card world, an authorized transaction can be reversed. This may happen, for example, when a fraudulent transaction has been charged against a customer's account, and the customer disputes the transaction. To avoid chargebacks, many merchants perform checks before accepting a transaction and refuse to accept it if suspicious. Sometimes blocked transactions are actually legitimate, and so this practice has the negative effect of preventing valid customers from completing their purchase. This type of chargeback does not occur with Interac Online Payment. The financial institution authorizes each payment, and guarantees payment to the merchant.