I recently bought a Sennheiser G2 radio mic system on ebay, and it was a copy, not made by Sennheiser.
How could I tell? Firstly, I was lucky enough to have several genuine ones to compare it with. Clues to a copy  I have noticed are:
1. The label on the rear of the transmitter has 'Assembied' not assembled  on it. The serial number was 111982.
2. The PSU label was shiny, with rounded corners but the originals are matt black with square corners.
3. The conical rubber  base of the beltpack antenna should not be smooth but be perforated all round.
4. The  flip cover on the transmitter was slightly marked in 2 places where the mould had not be quite filled properly and was a less than perfect fit.
5. The audio meter on the beltpack didn't show any level, and the peak light didn't light.
6. The tie clip mic was  nothing like the real sennheiser ME 4, not  round at the top and the plug was silver not the all black moulded plug of the original, plus the tie clip itself was the wrong type.
7. The ballistics of the AF meter on the receiver are slow, the real meter moves up and down much faster.
Overall however the coping was very good, especially the receiver. The trouble gone to by the forgers is truly astounding. I hope this may help other buyers.