Marko
take some simple points:
Your Nikon 70-200 f/2.8 VR II costs around 2400$ new. Lets suppose it is in best shape like new, but it´s a used lens so the value is around 2000 $.
On the other hand a Hasselblad 503CW with lens and A12 is around 2500 $ and up. I would say be careful.
there is always a reason why someone would leave 500 $ to you just so.
A Hasselblad is a mechanical Primadonna, if you touch her gently she will sing for a long time.
If you are a rough unhaptic motorical user, jamming the camera (put the lens on it uncocked) and just not using it smooth it will die on you.
if this is one which was used like this it may work, but the question is how long.
And ask the guy if there were any services done on the lens shutter (did it sit in a cupboard for some time unused : DON´T Buy it ! the oil will be stuck and the times are too slow)
or did the circuitry get some moisture some time, Blads HATE moisture, you will not see this from outside !!!!
If you want to get this item for the comfort of the easy exchange:
You could get the camera with a refund guarantee, take it to a service center , have it checked and if anything is OK keep it. Otherwise send it back.
My Proposal
Greetings from Munich
Stefan