Personal experiences with Russian Hasselblads.
My first camera was a 1981 Salyut ‘C’, bought on Ebay. Although it looked in very good order it clearly was not - the (non-matching) backs leaked and the shutter developed a fault after a few rolls of film. I had the camera repaired and upgraded but it was always mechanically rough and suffered incurable light leaks. Eventually it seized up and was deemed uneconomic to repair. However the quality of the best shots convinced me the cameras were worth the trouble of getting a decent one.
I have a number of years experience repairing Contax and Kiev RF’s so decided to buy a couple of spare scrap Salyut’s and attempt to build a replacement camera. I stripped the original Salyut ‘C’ and the general engineering finish was dismal. On stripping my parts cameras it became clear to me that various parts were re-designed over the years and some were incompatible. However I eventually managed to build a working camera. Sadly it did not prove to be reliable enough for serious use, but I had learned a huge amount about the cameras and knew exactly where the operating problems were with the design.
I had convinced myself that the early Salyut designs with pre-set diaphragms seemed to be built to a higher standard, based much more closely on the Hasselblad 1000f. I believe many of the engineering changes introduced by Arsenal have become the Achilles Heels in the later cameras.

I bought a 1970 Zenith 80 (UK imported and passed through Technical and Optical Equipment back in the 1970‘s). It came with it’s original pair of matching backs, box and leather case. This proved to be a very sound camera and was despatched to ARAX for:
1) Interior flocking,
2) Cloth blinds to be fitted,
3) Conversion to automatic diaphragm,
4) Full service.
The camera fully met my expectations, however the backs still leaked light. I totally stripped the backs using Hasselblad blueprints kindly supplied by Hasselblad. Sealing was patchy with the wool not going the full length of channels etc. I fully re-sealed the backs and converted the darkslide seals from the multi-part early Hasselblad type to the later foil seal. This has totally cured the light leaks. My confidence boosted, I decided to buy some more lenses to complete the outfit.

User hints and tips
The Kievaholic site http://kievaholic.com/kievaholics.html carries many hints and tips so I will limit this section to code red type tips which will help minimise malfunctions.
1) Winding the camera - it is absolutely critical to fully wind the camera. There will be tight spots and there should be a distinct ‘click’ at the end of the winding as the latch engages.
2) Winding should be a gentle, progressive operation, if possible in one go. A winding handle can help. Many cameras have been damaged by over enthusiastic winding.
3) UNDER NO CIRCUMSTANCES CHANGE SPEEDS BEFORE THE CAMERA IS WOUND, OR PART WAY THROUGH WINDING. It is very difficult to change the speeds before the camera is wound but is possible to accidentally pull the knob out of engagement as it is being wound. This will jam the camera and it will need partial stripping to repair.
4) Do not attempt to mount ‘preset’ diaphragm lenses on cameras designed for automatic diaphragms. They may go on but they very likely will not come off and foul the auto diaphragm mechanism.
5) Always keep the shutter pressed down until the ‘whizz’ of the slow speeds mechanism stops. This is critical for speeds less that 1:60th but I do this at all speeds. When the shutter is pressed down, a tongue locks elements of the stacked gears and prevents them moving during shutter run-off.
6) Have ANY mal-function investigated before further use, particularly the shutter sticking partly open. This is an easy problem to sort out but catastrophic damage can be caused by repeated winding/sticking.
7) Replace lens caps between shots - these cameras can suffer with light leaking past the shutter blinds and lightly fogging the film. Generally, light sealing and baffling is inadequate from new and deteriorates with age, when these problems become prevelant.
8) It is a good idea to occasionally cycle the camera with it’s back removed if it is to remain unused for a period. About half a dozen shots, three at speeds over 1:60th and then the other three at half a second - 1:30th will ensure the mechanism is exercised and lubricants kept in circulation.

Buying a camera
From personal experience I would suggest buying new from a reputable supplier such as ARAX. This way you have a warranty in case things go wrong.
To avail yourself of a range of cheap lenses it may be best to stick with the older type lens mount - P6 type lenses are more expensive.

EBAY purchases really are a risk; often the maths of buying/importing a camera, then finding it needs a service, works out to be more than buying a new camera. I know that, for the money I have spent on two cameras and two repairs, I could have bought a new camera from ARAX.