If you're searching for Sennheiser microphones on eBay, (E822II-S, E828S, E845S) you should be aware that some people are selling fakes (and unfortunately getting away with it). This is probably true also for other brands, such as Shure.
I recently purchased a  Sennheiser E845 from a italian seller, to be used in voice recognition.
Here are some signs I picked up on:
1. The general appearance of the photo on the box was a little cloudy (compared to a real box that I purchased later from an authorized dealer)
2. The declared characteristics on the box were; Cardioid Vocal Mic (the real one should be a Super Cardioid, instead); frequency characteristics 80-15 kHz (the real one should have 40-16 kHz)
3. Inside the box there was a leaflet (with the same cloudy appearence of the box) with the following characteristics; 
    a) Freq.resp. 40-16 kHz (different from the one declared on the outer box). 
    b) The polar diagram was obviously different from the one reported on the Sennheiser site,  and it was not a supercardioid one.
    c) sensitivity 1.5mv/Pa (1.8 the one reported on the site)
    d) nominal impedance 350 ohm, but on the mike was written 600 ohm instead.
4. In the leaflet there were reported also other microphones (E822II-S, E828S, E845S) and all of them were uniformly described as having the very same characteristics and performances !!.
4. The weight of the suspected fake was 331g (330 the real one), the dimensions were 48 X 18 (46 X 18,5 the true one)
5. There was no the guarantee leaflet, as in the other true mike I bought from an authorized dealer.
6. There was no pouch and clamp, as described on the Sennheiser site, but the mike was simply wrapped in pluriball.

Upon receiving the mike, it was not easily recognized by me that it was fake, because it has a very good appearance.
After looking over these indicators, I suspected that the seller is actually selling fakes.
I hope this help