...although the now defunct Distance Selling Regulations [Consumer Protection (Distance Selling) Regulations 2000], having been superseded by The Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013, did not (and does not) apply to private purchases.
Where the regulations do apply, i.e. non-exempted purchases from a trader, there is no absolute right to receive a full refund for a change of mind;
refundable delivery costs are limited to the cheapest standard delivery rate offered, e.g. if you upgrade from 2nd Class to 1st Class, the refund will be 2nd Class only;
refund of purchase price can be reduced where goods show signs of unreasonable use that has led to diminished value (deductions cannot be made for removal from packaging or having been tried/checked).
Also, there would be no automatic cover of the return postage, provided that is clearly stated in the original listing.
Refunds for faulty goods are not limited by the above.