Returning goods - this is a guide for the seller, not the consumer - so 'you' refers to the seller.
Only if it is covered in the contract and the written information
can you require the consumer to pay for the cost of returning
the ordered goods. If the consumer then fails to return the
goods, or sends them at your expense, you can charge them
the direct cost to you of the return, even if you have already
refunded the consumer’s money. You are not allowed to
make any further charges, such as a restocking charge or an
administration charge.
If you do not include these details in the required written
information then you cannot charge anything. You can never
require consumers to pay the cost of returning substitute
goods.
If the goods are faulty or do not comply with the
contract, you will have to pay for their return whatever the
circumstances.