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unholyangel

OP bear in mind in order to make a deduction under the quoted legislation, you would have had to have complied with that legislation.

(9) If (in the case of a sales contract) the value of the goods is diminished by any amount as a result of handling of the goods by the consumer beyond what is necessary to establish the nature, characteristics and functioning of the goods, the trader may recover that amount from the consumer, up to the contract price.

(10) An amount that may be recovered under paragraph (9)—

(a)may be deducted from the amount to be reimbursed under paragraph (1);
(b)otherwise, must be paid by the consumer to the trader.

(11) Paragraph (9) does not apply if the trader has failed to provide the consumer with the information on the right to cancel required by paragraph (l) of Schedule 2, in accordance with Part 2.


(12) For the purposes of paragraph (9) handling is beyond what is necessary to establish the nature, characteristics and functioning of the goods if, in particular, it goes beyond the sort of handling that might reasonably be allowed in a shop.

Paragraph (l) of schedule 2 tells us:

(l)where a right to cancel exists, the conditions, time limit and procedures for exercising that right in accordance with regulations 27 to 38;

You can read through regulations 27 to 38 yourself here:
http://www.legislation.gov.uk/uksi/2013/3134/part/3/made

In other words, you need to have informed them that under the CCRs, they have the right to cancel within 14 days but that if they diminish the value with unreasonable handling, you'll deduct it from their refund.