As far as I know there's no completely red DS Lite except the limited edition Mario Red DS Lite. Is your friend's unit look like this?

No. The whole thing is red. Without the M logo
guys, i doubt the DS is a fake just based on the barcode
Mine was bought few years ago, US version, black, and there's a barcode on the serial number, and I even successfully registered the serial at Nintendo Club
The website vildante provided doesn't really proves the existence of FAKE DS, the so called FAKE DS actually is US region DS, where can be seen clearly from the serial number, and the one they are comparing is the UK version. If you look under the Jap version, again it's different.
The website call it fake just bcos of bad 3rd party power adaptor. Remember the US DS came with 110V power adapter only, whereas UK is using 220/240V power, so in order to sell the US set in UK, you'll have to replace the 110V with the 220V 3rd party adaptor.
In the case of TS, i believe the DS is a GENUINE NDS from NINTENDO, but most likely is a refurbished set sold as new, some of the refurbished set they changed the case and the buttons, and also the battery.
one way to check if it's refurbished or not, check the screws, got any scratched mark on it or not, brand new one should have any, and also open up the battery compartment and check the battery to see if it's genuine battery from Nintendo. and also check the packaging.
There's no FAKE NDS, there's only re-furbished NDS sold as new.
But if confirms it's re-furbished, then the seller also is a conman and doesn't deserve sell his items here in LYN anymore.
Its not the matter of genuine or fake.
Its the matter of warranty and trustworthy. He's selling faulty set and he don't want to give me any service.
Yet, I just realize that he didn't ever give me a warranty card.