Opinion Road

When I buy a pair of Sennheiser’s on EBay, am I getting a knock-off (counterfeit), a factory ‘back door’ model, or the genuine product? I’ve gone through quite a few pairs of Sennheiser’s CX200, CX300 II and one CX 500 ear-canal earphones, most of which (though not all) have been bought through EBay resellers. For the most part, they have been good quality – with the occasional store-bought pair being indistinguishable in listening or packaging quality.