As a small business, every time we receive a ticket payment, a number of parties charge us fees on those payments, these include the card processor (merchant fees), the system that takes the payment (PayPal or SagePay) and then banking fees. All of these steps very quickly add up and if we have to process a refund we don't get many (if any) of these fees back.
In addition, every refund takes up a small amount of staff administrative time processing the refund as a manual process.
Therefore we retain a small and reasonable administration fee based on the above costs when processing any ticket cancellations in order to cover these costs when you cancel. This fee is clearly defined when you book and in your confirmation emails.