Is it an obligation to show the correct return fee in the confirmation? We use volume-based return fees, not one fee for all.
The return cost must be written out clearly in your terms and conditions. As long as it is clearly stated there, you can refer to it – a volume-based fee structure is acceptable if it is explained. What you cannot do is hide the existence of a return cost or leave it ambiguous. If your fee varies by order size, state that clearly in your terms before the customer completes the purchase.