I got my Zorki 6 from this seller and I was quite happy with the service.
https://www.ebay.ca/str/ussrphotoworldWhile I haven't had time to put a full roll through the camera, everything looks promising.
He answers quite rapidly to emails, so feel free to ask him any question you want.
For rangefinders, there are a few questions to ask:
-How bright is the rangefinder double image
-Are there any pinholes in the shutter curtains
-Do the shutter speeds sound consistant
Once this is answered, you know you want to buy.
He does have a Zorki 4 at an affordable price that looks really nice. He also has some FEDs that look good. I have a Fed 5v (or 5B if you read Cyrillic).
This is pretty much the top of the line for the FED cameras. The only drawbacks with this one is that the ergonomics are a bit crap and it lacks strap lugs. But on the up side it has full set of slow speeds, something the Zorkis lack.
But for all those cameras, make sure you also get a set of cheap soft release buttons from Aliexpress! Your fingers will thank me for it
