I and my friends have done dozens if not hundreds of successful transactions with FSU sellers, some amounting to hundreds of dollars at a pop. I too, will also recommend FedKa. Yuri simply does it right.
I will wholeheartedly recommend CUPOG in Slovakia, who may be the finest seller, of any kind, on Ebay. When he says a camera has been CLA'd it has been and he tells you with a sticker inside the camera when and by whom and CUPOG stands behind it. His offerings have been varying widely but his quality is always as he clearly states. Best possible service and communications. A true gentleman.
Arax (Ukraine) and
Kiev Camera (US) have been perfect for me also, but most of my purchases from them have been superbly tuned and adjusted new items. I buy mostly new stuff. and in the FSU 15 year old New-Old Stock happens often, but most of what buy is still in production. It is not impossible to find NOS Kiev 4x cameras and lenses. During the transition in the late 90's and early 2000's many bills were paid with warehouses full of cameras and other items which were manufactured to production quotas instead of consumer demand.
True Leica copies ended decades ago but there is a huge supply, and in almost every case the "improved" models are mechanically much better, even though the later cameras such as the Fed 5 look awkward, ungainly and starkly ugly, they do work as competent photographic devices.
I have had good results with a few others as well.
Since I, by choice, (I do have others) use KIEV MF cameras for professional projects there is no room for problems. Gevorg (Arax) and Michael (Kiev Camera) are two I can depend on if there should be a problem. Mike is in the US and both are easily reachable. ARAX even posts their hours and notifies about holidays and vacations by e-mail.
There is even a reliable (and very affordable) repair service in Brooklyn NY. Eddie Smoloff, 718-622-5373 originally worked for Arsenal (KIEV) factory. Others in New Jersey, Holland and Germany.
Two terriffc resources are:
http://forums.delphiforums.com/kievreport/start
and
http://www.kievaholic.com/
Both are heavily skewed toward the Medium Format cameras but 35mm is there, just look for it.
For research on all things FSU,
Nathan Dayton's Commie Camera site
Fred