Overheads are fees that generally apply to the entire order.
When you create overheads, you need to select to what kind of order the fee will apply:
Booking/Sale => reservation/sales
Refund by organisation / contact => refund requested by the customer or the organiser (see below)
Exchange by organisation / contact => exchange requested by the customer or the organiser (see below) - an exchange implies that new tickets are issues against the refunded ones
Option => when tickets are requested
Difference between organisation/customer. And field where the Reason for refund/exchange can be put.
You can also decide that only a selected payment method will trigger overheads => example if you want that the use of a specific credit card on the ticketshop generates fees for the purchaser.
You can associate overheads with specific refund reasons.