A payment service is configured to support purchase transactions generated by merchant point-of-sale (POS) devices. As transactions are conducted, the payment service evaluates, for each transaction, the risk of subsequent chargeback. The payment service then notifies the merchant that expedited payment is available for transactions having low risks of chargeback. The merchant can select a user interface element to initiate expedited payment of the transactions via a debit card linked to the merchant's bank account. Other transactions are settled in a non-expedited manner, using a batch funds transfer.