authenticity of ebay products

I've recently been buying Turnbull, Sulka, Hilditch, and Charvet ties on ebay..I've heard it said that counterfeit Hermes ties have flooded the ebay market..how can one be reasonably confident that one is buying a Turnbull and Asser(for example)tie?...I suspect even the sellers themselves might not be aware if they come into possession of what appears to be a product with a Turnbull lable on it..any thoughts?