We add a 30-cent ($0.30, or about .20 UK pound) processing fee to the actual print cost we pay our printer. All print costs you see displayed here on the marketplace include this processing fee. Thus, a print title that has a base print cost of $3.70 will have a total print cost of $4.00. We add this fee to cover credit card or Paypal payment processing fees.
For those who'd like more detail: When a print title sells for $10, where $4 of that is the actual (base) print cost, we pay a processing fee on the entire $10. For the $6 margin of that, which we split with you, the payment processing on the $6 comes out of our cut on the $6 margin. Since the $4 is our direct pass-through cost, though, we have no fee to cover the payment processing on the $4. Hence, we cannot be sure of recapturing those costs on our share of the margin because you may choose to set a very low (or even zero) margin on a title, so we assess the processing fee to avoid losing money on every sale of some low-priced products.