I sell designer clothing on ebay. My sales are over $1M annually and most of it is from designer clothing. For obvious reasons my buyers want to be sure that they are getting authentic merchandise. Recently a buyer left me negative feedback (without contacting me first) stating that the item they purchased was counterfeit. I offered to send them my invoices as proof that the item is authentic but they don't want to change the feedback. I only received one such feedback (claiming counterfeit) and it was a few years back. At this point, I'm worried this one will scare away buyers. Do I have a case for libel? If so, how do I go about it?