This is incorrect. Under the distance selling regulations the seller must refund the full amount and impose no extra charges: "On the cancellation of a contract under regulation 10, the supplier shall reimburse any sum paid by or on behalf of the consumer under or in relation to the contract to the person by whom it was made free of any charge" assuming that the buyer has taken "reasonable care of them". Under the sale of goods act you have a right to open the box and inspect (including use) items "when the seller tenders delivery of goods to the buyer, he is bound on request to afford the buyer a reasonable opportunity of examining the goods for the purpose of ascertaining whether they are in conformity with the contract"
Also from the OFT guide on the DSR for businesses (
http://www.oft.gov.uk/shared_oft/bus...ral/oft913.pdf) :
"You are not allowed to make any further charges, such as a restocking charge or an administration charge."