Mail order customers have 14 days (according to the EU Distance Selling Regulations) in which to cancel an order without having to state a reason. I think they have another 14 days to return the goods (but don't quote me). The customer has to pay the cost of return carriage if it's in the seller's terms and conditions, but the seller *cannot charge a restocking fee or administration charge*.
I work in the retail business and this is quite correct.