A complicated story! The goods were a pressure regulator and damper for the petrol engine in a classic Porsche sports car which were advertised as being suitable for my particular model and others. (Cost with delivery and UK Vat almost £500 GBP). On arrival and fitting it was evident that they did not operate at the pressure specified by Porsche. I notified the supplier (in Germany) of that fact, questioned their suitability, and lodged a claim under the returns policy well within the 30 day period). The supplier assured me that the products were suitable and no problems had been experienced with them before and his supplier was very reliable. On the basis of this assurance, which I expressly made in email correspondence with the supplier through eBay, I cancelled my returns application. A short while afterwards, and after only 67 miles of use, the regulator failed completely, leaving me stranded, but more importantly creating a serious fire hazard from leaking petrol (gas). On reporting this to the supplier and asking for a refund I was offered a replacement, which I declined, as the same thing would be likely to occur again unless it was up to the correct specification. Supplier suggested some unspecified defect in my engine might have caused the failure and has gone quiet, despite reminders. I can find nothing on eBay website to fit the circumstances of being beyond the guaranteed returns period, and have been unable to contact any person at eBay to discuss. The products were not as advertised, were defective, and not fit for purpose. All the circumstances are set out in detail in the email correspondence through eBay. I will refer this to my credit card provider as suggested by the first responder, for which thanks.
