If you change your mind about an item that you have purchased, it must be returned within seven days of delivery, in new condition, with tags still attached. Buyer will be responsible for return postage. If item is received back in new condition a full refund will be made.
Where a purchase has qualified for free postage and is returned because the buyer has changed their mind about the item, original P&P charge will be deducted from refund value.
Faulty items can be returned within your statutory rights : https://www.gov.uk/accepting-returns-and-giving-refunds