I recently found a fake Contax being auctioned on Ebay and fetching a good price. It must be true that wherever there is a thing of value there will also be fakes. The following pictures were lifted from the auction page and each is explained to show how you can diagnose the clever Contax fake.
The first picture demonstrates that a real Contax front plate will definitely fit on a Kiev. Notice the Kiev flash synchronization socket on the right and the style of the lightmeter adjustment knob. The Kiev camera has a lightmeter knob on its Contax III type models that is a copy of the knob on the Contax IIIa type models. It also has a Contax IIIa type rising rewind knob.
This camera has a Contax front plate and a Zeis 50mm Collapsable Sonnar, but it's no Contax.
This is a Kiev bottom plate. The Contax plate has the famous flip out stabilizer and decorative raised bezels around the closing bails. Kiev closing bails are also highly polished. Notice there is no Zeiss logo stamp on the leather.
The small meter adjustment screw bezel and the cocked meter top plate are Kiev givaways.
The Kiev uses little round headed screws to hold the meter top plate and the front plate onto the camera. Notice how flat headed Zeiss screws have been used on this camera to help disguise it.
Finally, can you see the little Russian word following the "500" on the film speed setting dial?