Click on this link to learn how to find the serial number of your AirPods --> Find the serial number of your AirPods - Apple Support
Enter the serial number in this link --> Check Your Service and Support Coverage - Apple Support - Check Your Service and Support Coverage - Apple Support
Does it find them? If yes then at least the serial number is real, but fake copies can have real serial numbers that might well, of course, be reported as valid. If you take them to Apple they may be able to tell the difference. The bottom line is the only real way to be sure Airpods are not fake is to only buy them from Apple or an Apple Authorized retailer. --> Find Locations
If it says the serial number was replaced* that likely means they were reported as defective and Apple replaced them but they were not returned to Apple as required, or they were reported lost or stolen from stock or during shipping. No support or service is available for them.
" The product has been replaced by our record, Please provide the serial number for your replacement product to find the support and warranty coverage information"