You can cancel an order yourself, from your order page, while it is awaiting a quote or awaiting your payment, up until you upload a payment confirmation. There is no charge and nothing is owed.
Once you have uploaded a payment confirmation, cancellation is handled by us rather than from your side: contact us through your order messages. By that point your funds may already have left your account, even if we have not yet verified them, so we take it from there and reconcile any payment you have made. Where we have verified your payment, we refund the full amount to your account credit for use toward a future order.
Once we have purchased your items, an order cannot be cancelled: your funds are committed with the seller, and the inspection and, where relevant, the final-sale position apply.
Refunds from a cancellation are always to account credit, never cash. Account credit explained covers how to use it.
See: Terms of Service, section 8 (Refunds and Cancellations).