Thanks... I'll do just that!

Hello everyone - I hope somebody out there can help me! I recently ordered a second hand Laptop screen from eBay (Business Seller) at a cost of £40. It was received faulty so they asked be to return it – It cost me £10 in postage. The shop said they would send me a compatible replacement. Unfortunately, the one received could not be fitted properly and it did not fit the description of the original item I ordered. This screen was returned at a further cost of £10 At this point the staff were very helpful and, although I had to wait a couple of weeks, they finally refunded me my original £40 payment. I requested that in view of the full circumstances they should also refund me the total cost of return postage (£20) for the faulty/incorrect items. The shop replied: We do not cover return postage... see our site for T&C. How can we refund what we have have not received? You asked for a refund, you have a refund – Please be aware that the Sale of Goods differs as the items were second hand. I response I said: Second-hand should not mean second-rate Even if the item's second-hand or reduced, it doesn't mean you get second-rate consumer rights, except where the seller points out the specific problems before the item was bought. As you have sent faulty/wrong items then I’m entitled to 100% refund of cost and postage! The shop said I’m talking rubbish and if I took it to Small Claims I would lose and I will be responsible for their legal fees. My question is... are the shop right in what they are saying or are they just trying to scare or intimidate me? I know it only £20 but that is a lot to me at the moment! Kindest regards,