Sold a pair of unworn Clarks ankle boots on ebay (auction). Boots are size 7. According to ebay conversion chart this is 40. So I sold it as size 7 (40). Seller contacted me that shoes are to big and she believes they are more a 41. Replied that they are labelled size uk7 and that I sold them in good faith but offered her refund of the price of boots, not postage. She argues a size 7 is a European 41 and I should refund full postage both ways as well. In fact a size 7 uk is somewhere between a European 40 and 41 and I feel as a uk buyer of uk sized shoes she should know her size. It states nowhere on the shoes that they are 40 or 41. What should I do?