The irreversibility of payments in nearly all crypto systems does NOT prevent providing a refund to a customer. That can always be done by making a new payment to the customer.
One might argue that crypto makes customers unable to demand a refund, or that it is impossible to send a refund to a customer who is so anonymous that the merchant cannot even communicate with them, but these are less obviously a "no-no" for a business.
One might argue that crypto makes customers unable to demand a refund, or that it is impossible to send a refund to a customer who is so anonymous that the merchant cannot even communicate with them, but these are less obviously a "no-no" for a business.