The most important way to ensure product authenticity is to always buy from an authorized dealer. If you have already purchased a product you can check it's authenticity by using the Product Authenticity Portal located on our website: http://qr-sennheiser.com/index.php?id=5&L=1&id=5
We maintain a list of NON-authorized dealers at the following link: (http://en-us.sennheiser.com/service-support/non-authorized-dealer-list). Please do not buy from these dealers as they may be selling counterfeit products and any products they sell will not be covered under Sennheiser's warranty.
As non-authorized dealers change business names and operations on a daily basis, this list of non-authorized is not all-inclusive. Please use the Product Authenticity Portal to ensure you are buying a genuine Sennheiser product.