VATRES3250 - Personal exports - retail exports: How the scheme works: Administration charges
The retailer usually makes a charge to cover administrative and handling expenses. Larger retailers usually calculate the charge on a sliding scale. Smaller retailers may charge a set amount regardless of the purchase value. Administration charges can be the source of complaint from customers. Because of this, the amount of the administrative fee and net refund due to the traveller must be clearly shown on the VAT refund document. Whether the retailer charges an administration fee and the amount of such a fee is entirely a commercial decision. HMRC cannot intervene if disputes arise between retailers and their customers.
The refund companies base their business on the commission which they charge the traveller for administrating the refund.