A fake Flash Voyager will have;
No etched numbers on the USB port
No blue L.E.D
The device will not as "Corsair Flash Voyager USB Device" in Device manager
The end of the unit will be soft/bendy
The colours at the side (Red and Blue) rub off easily.
Advertised device capacity is modified to fix a certain amount of data before overwriting it.
You can use H2testw 1.4 to test the drives capacity.