Yes, any purchase from your customers can be refunded from the Orders section in the store backend. When you cancel an entire order, we also refund the fee we originally took on that order based on your account plan.
You are also able to refund individual items within an order (to handle returns or order modifications based on custom support inquiries, for instance).
Refunds are free through Stripe. For more details on their disputes/chargebacks policies view https://stripe.com/help/disputes.