How to know if a Galaxy Note is a real one?
Grab MAC address of Wi-Fi adapter of device. Go to Settings ~> Wireless and Network ~> Wi-Fi Settings and tap/press options key. Then, tap Advanced. Here, you can get MAC address. The method can vary based on firmware.
Look up this MAC address at http://www.techzoom.net/tools/check-mac.en or http://www.coffer.com/mac_find/ . If device isn't legitimate, you can detect here.