the european directives which still apply here, for the time being, do allow people buying on auction sites to change their mind, so long as they do not have the opportunity to inspect the goods in person beforehand, and/or basically that the auction is not taking part in a physical auction house. It gets a bit more muddy for private sellers vs private buyers and the listing wording comes into play, which unless the OP gives us a copy, we are in the dark over.
The County Court needs to see evidence of your losses and how they are reasonably attributed to the person you are claiming against. Then you also have to demonstrate what steps you have taken to avoid the case going to court in the first place. One of the first things the County Court looks at are whether there has already been any form of arbitration that affects their ability to rule on the case. Ebay's internal arbitration is such an example.