I sold a modified second hand bicycle the buyer used PayPal. I explained I still had the original parts (I bought it second hand) I sent detailed photos to the buyer and explained he could return the bike to it's original condition if he preferred. He stripped it, repainted it then said the gear shifter was the wrong brand. I explained he had everything in the advert. PayPal are now billing me for a part costing£120 which he didn't need and put me in dispute. How can this be right?