Your MacBook Pro’s serial number is critical for service, security, and resale. You now know —from the simple Apple menu to the advanced Terminal command. If your machine is running, use "About This Mac." If it is dead, check your Apple ID online or the original box.
If you follow the methods above and see "Unavailable" or "To be filled by O.E.M." (Original Equipment Manufacturer), this is a major red flag. It usually means one of two things: how to check serial number macbook pro