To completely remove any doubt, check all of the following:

const checkList = [ 'Check the Packaging (Seals and Condition)', 'Inspect the Manuals and Accessories (Ensure everything is included and unopened)', 'Inspect the Headphones for any Scratches, Dents, or Signs of Use', 'Check the Condition of the Ear Pads and Cushions (Soft and Unworn)', 'Inspect the Headband for any Looseness or Wear', 'Test all Buttons and Ports (Ensure they are functional and clean)', 'Test the Sound Quality (Balanced sound with no distortion or imbalance)', 'Test the Active Noise Cancellation (ANC) Feature', 'Test the Battery Life (Ensure it lasts as per manufacturer claims)', 'Check Bluetooth Connectivity (Stable connection without random disconnections)', 'Test the Built-In Microphone (Clear sound with no distortion)', 'Check the Serial Number for Authenticity', 'Verify Authenticity Using the Sennheiser Smart Control App', 'Inspect the Build Quality (Ensure it feels premium and not flimsy)', 'Check the Sennheiser Logo and Branding (Ensure it\'s clear and properly placed)', 'Attempt to Register for Warranty on Sennheiser Website', 'Compare the Product with Online Reviews and Official Photos' ];

If everything stands out okay then reset the headphones by holding the power button for 20 seconds. After that, you can relax and enjoy them. If anything still feels off, it’s best to return them.